Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1295 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
new file mode 100644
index 000000000..3f479483d
--- /dev/null
+++ b/drivers/gpu/drm/drm_probe_helper.c
@@ -0,0 +1,1295 @@
+/*
+ * Copyright (c) 2006-2008 Intel Corporation
+ * Copyright (c) 2007 Dave Airlie <airlied@linux.ie>
+ *
+ * DRM core CRTC related functions
+ *
+ * Permission to use, copy, modify, distribute, and sell this software and its
+ * documentation for any purpose is hereby granted without fee, provided that
+ * the above copyright notice appear in all copies and that both that copyright
+ * notice and this permission notice appear in supporting documentation, and
+ * that the name of the copyright holders not be used in advertising or
+ * publicity pertaining to distribution of the software without specific,
+ * written prior permission.  The copyright holders make no representations
+ * about the suitability of this software for any purpose.  It is provided "as
+ * is" without express or implied warranty.
+ *
+ * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+ * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
+ * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
+ * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
+ * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+ * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
+ * OF THIS SOFTWARE.
+ *
+ * Authors:
+ *      Keith Packard
+ *	Eric Anholt <eric@anholt.net>
+ *      Dave Airlie <airlied@linux.ie>
+ *      Jesse Barnes <jesse.barnes@intel.com>
+ */
+
+#include <linux/export.h>
+#include <linux/moduleparam.h>
+
+#include <drm/drm_bridge.h>
+#include <drm/drm_client.h>
+#include <drm/drm_crtc.h>
+#include <drm/drm_edid.h>
+#include <drm/drm_fourcc.h>
+#include <drm/drm_modeset_helper_vtables.h>
+#include <drm/drm_print.h>
+#include <drm/drm_probe_helper.h>
+#include <drm/drm_sysfs.h>
+
+#include "drm_crtc_helper_internal.h"
+
+/**
+ * DOC: output probing helper overview
+ *
+ * This library provides some helper code for output probing. It provides an
+ * implementation of the core &drm_connector_funcs.fill_modes interface with
+ * drm_helper_probe_single_connector_modes().
+ *
+ * It also provides support for polling connectors with a work item and for
+ * generic hotplug interrupt handling where the driver doesn't or cannot keep
+ * track of a per-connector hpd interrupt.
+ *
+ * This helper library can be used independently of the modeset helper library.
+ * Drivers can also overwrite different parts e.g. use their own hotplug
+ * handling code to avoid probing unrelated outputs.
+ *
+ * The probe helpers share the function table structures with other display
+ * helper libraries. See &struct drm_connector_helper_funcs for the details.
+ */
+
+static bool drm_kms_helper_poll = true;
+module_param_named(poll, drm_kms_helper_poll, bool, 0600);
+
+static enum drm_mode_status
+drm_mode_validate_flag(const struct drm_display_mode *mode,
+		       int flags)
+{
+	if ((mode->flags & DRM_MODE_FLAG_INTERLACE) &&
+	    !(flags & DRM_MODE_FLAG_INTERLACE))
+		return MODE_NO_INTERLACE;
+
+	if ((mode->flags & DRM_MODE_FLAG_DBLSCAN) &&
+	    !(flags & DRM_MODE_FLAG_DBLSCAN))
+		return MODE_NO_DBLESCAN;
+
+	if ((mode->flags & DRM_MODE_FLAG_3D_MASK) &&
+	    !(flags & DRM_MODE_FLAG_3D_MASK))
+		return MODE_NO_STEREO;
+
+	return MODE_OK;
+}
+
+static int
+drm_mode_validate_pipeline(struct drm_display_mode *mode,
+			   struct drm_connector *connector,
+			   struct drm_modeset_acquire_ctx *ctx,
+			   enum drm_mode_status *status)
+{
+	struct drm_device *dev = connector->dev;
+	struct drm_encoder *encoder;
+	int ret;
+
+	/* Step 1: Validate against connector */
+	ret = drm_connector_mode_valid(connector, mode, ctx, status);
+	if (ret || *status != MODE_OK)
+		return ret;
+
+	/* Step 2: Validate against encoders and crtcs */
+	drm_connector_for_each_possible_encoder(connector, encoder) {
+		struct drm_bridge *bridge;
+		struct drm_crtc *crtc;
+
+		*status = drm_encoder_mode_valid(encoder, mode);
+		if (*status != MODE_OK) {
+			/* No point in continuing for crtc check as this encoder
+			 * will not accept the mode anyway. If all encoders
+			 * reject the mode then, at exit, ret will not be
+			 * MODE_OK. */
+			continue;
+		}
+
+		bridge = drm_bridge_chain_get_first_bridge(encoder);
+		*status = drm_bridge_chain_mode_valid(bridge,
+						      &connector->display_info,
+						      mode);
+		if (*status != MODE_OK) {
+			/* There is also no point in continuing for crtc check
+			 * here. */
+			continue;
+		}
+
+		drm_for_each_crtc(crtc, dev) {
+			if (!drm_encoder_crtc_ok(encoder, crtc))
+				continue;
+
+			*status = drm_crtc_mode_valid(crtc, mode);
+			if (*status == MODE_OK) {
+				/* If we get to this point there is at least
+				 * one combination of encoder+crtc that works
+				 * for this mode. Lets return now. */
+				return 0;
+			}
+		}
+	}
+
+	return 0;
+}
+
+static int drm_helper_probe_add_cmdline_mode(struct drm_connector *connector)
+{
+	struct drm_cmdline_mode *cmdline_mode;
+	struct drm_display_mode *mode;
+
+	cmdline_mode = &connector->cmdline_mode;
+	if (!cmdline_mode->specified)
+		return 0;
+
+	/* Only add a GTF mode if we find no matching probed modes */
+	list_for_each_entry(mode, &connector->probed_modes, head) {
+		if (mode->hdisplay != cmdline_mode->xres ||
+		    mode->vdisplay != cmdline_mode->yres)
+			continue;
+
+		if (cmdline_mode->refresh_specified) {
+			/* The probed mode's vrefresh is set until later */
+			if (drm_mode_vrefresh(mode) != cmdline_mode->refresh)
+				continue;
+		}
+
+		/* Mark the matching mode as being preferred by the user */
+		mode->type |= DRM_MODE_TYPE_USERDEF;
+		return 0;
+	}
+
+	mode = drm_mode_create_from_cmdline_mode(connector->dev,
+						 cmdline_mode);
+	if (mode == NULL)
+		return 0;
+
+	drm_mode_probed_add(connector, mode);
+	return 1;
+}
+
+enum drm_mode_status drm_crtc_mode_valid(struct drm_crtc *crtc,
+					 const struct drm_display_mode *mode)
+{
+	const struct drm_crtc_helper_funcs *crtc_funcs = crtc->helper_private;
+
+	if (!crtc_funcs || !crtc_funcs->mode_valid)
+		return MODE_OK;
+
+	return crtc_funcs->mode_valid(crtc, mode);
+}
+
+enum drm_mode_status drm_encoder_mode_valid(struct drm_encoder *encoder,
+					    const struct drm_display_mode *mode)
+{
+	const struct drm_encoder_helper_funcs *encoder_funcs =
+		encoder->helper_private;
+
+	if (!encoder_funcs || !encoder_funcs->mode_valid)
+		return MODE_OK;
+
+	return encoder_funcs->mode_valid(encoder, mode);
+}
+
+int
+drm_connector_mode_valid(struct drm_connector *connector,
+			 struct drm_display_mode *mode,
+			 struct drm_modeset_acquire_ctx *ctx,
+			 enum drm_mode_status *status)
+{
+	const struct drm_connector_helper_funcs *connector_funcs =
+		connector->helper_private;
+	int ret = 0;
+
+	if (!connector_funcs)
+		*status = MODE_OK;
+	else if (connector_funcs->mode_valid_ctx)
+		ret = connector_funcs->mode_valid_ctx(connector, mode, ctx,
+						      status);
+	else if (connector_funcs->mode_valid)
+		*status = connector_funcs->mode_valid(connector, mode);
+	else
+		*status = MODE_OK;
+
+	return ret;
+}
+
+static void drm_kms_helper_disable_hpd(struct drm_device *dev)
+{
+	struct drm_connector *connector;
+	struct drm_connector_list_iter conn_iter;
+
+	drm_connector_list_iter_begin(dev, &conn_iter);
+	drm_for_each_connector_iter(connector, &conn_iter) {
+		const struct drm_connector_helper_funcs *funcs =
+			connector->helper_private;
+
+		if (funcs && funcs->disable_hpd)
+			funcs->disable_hpd(connector);
+	}
+	drm_connector_list_iter_end(&conn_iter);
+}
+
+static bool drm_kms_helper_enable_hpd(struct drm_device *dev)
+{
+	bool poll = false;
+	struct drm_connector *connector;
+	struct drm_connector_list_iter conn_iter;
+
+	drm_connector_list_iter_begin(dev, &conn_iter);
+	drm_for_each_connector_iter(connector, &conn_iter) {
+		const struct drm_connector_helper_funcs *funcs =
+			connector->helper_private;
+
+		if (funcs && funcs->enable_hpd)
+			funcs->enable_hpd(connector);
+
+		if (connector->polled & (DRM_CONNECTOR_POLL_CONNECT |
+					 DRM_CONNECTOR_POLL_DISCONNECT))
+			poll = true;
+	}
+	drm_connector_list_iter_end(&conn_iter);
+
+	return poll;
+}
+
+#define DRM_OUTPUT_POLL_PERIOD (10*HZ)
+static void reschedule_output_poll_work(struct drm_device *dev)
+{
+	unsigned long delay = DRM_OUTPUT_POLL_PERIOD;
+
+	if (dev->mode_config.delayed_event)
+		/*
+		 * FIXME:
+		 *
+		 * Use short (1s) delay to handle the initial delayed event.
+		 * This delay should not be needed, but Optimus/nouveau will
+		 * fail in a mysterious way if the delayed event is handled as
+		 * soon as possible like it is done in
+		 * drm_helper_probe_single_connector_modes() in case the poll
+		 * was enabled before.
+		 */
+		delay = HZ;
+
+	schedule_delayed_work(&dev->mode_config.output_poll_work, delay);
+}
+
+/**
+ * drm_kms_helper_poll_enable - re-enable output polling.
+ * @dev: drm_device
+ *
+ * This function re-enables the output polling work, after it has been
+ * temporarily disabled using drm_kms_helper_poll_disable(), for example over
+ * suspend/resume.
+ *
+ * Drivers can call this helper from their device resume implementation. It is
+ * not an error to call this even when output polling isn't enabled.
+ *
+ * Note that calls to enable and disable polling must be strictly ordered, which
+ * is automatically the case when they're only call from suspend/resume
+ * callbacks.
+ */
+void drm_kms_helper_poll_enable(struct drm_device *dev)
+{
+	if (!dev->mode_config.poll_enabled || !drm_kms_helper_poll ||
+	    dev->mode_config.poll_running)
+		return;
+
+	if (drm_kms_helper_enable_hpd(dev) ||
+	    dev->mode_config.delayed_event)
+		reschedule_output_poll_work(dev);
+
+	dev->mode_config.poll_running = true;
+}
+EXPORT_SYMBOL(drm_kms_helper_poll_enable);
+
+/**
+ * drm_kms_helper_poll_reschedule - reschedule the output polling work
+ * @dev: drm_device
+ *
+ * This function reschedules the output polling work, after polling for a
+ * connector has been enabled.
+ *
+ * Drivers must call this helper after enabling polling for a connector by
+ * setting %DRM_CONNECTOR_POLL_CONNECT / %DRM_CONNECTOR_POLL_DISCONNECT flags
+ * in drm_connector::polled. Note that after disabling polling by clearing these
+ * flags for a connector will stop the output polling work automatically if
+ * the polling is disabled for all other connectors as well.
+ *
+ * The function can be called only after polling has been enabled by calling
+ * drm_kms_helper_poll_init() / drm_kms_helper_poll_enable().
+ */
+void drm_kms_helper_poll_reschedule(struct drm_device *dev)
+{
+	if (dev->mode_config.poll_running)
+		reschedule_output_poll_work(dev);
+}
+EXPORT_SYMBOL(drm_kms_helper_poll_reschedule);
+
+static enum drm_connector_status
+drm_helper_probe_detect_ctx(struct drm_connector *connector, bool force)
+{
+	const struct drm_connector_helper_funcs *funcs = connector->helper_private;
+	struct drm_modeset_acquire_ctx ctx;
+	int ret;
+
+	drm_modeset_acquire_init(&ctx, 0);
+
+retry:
+	ret = drm_modeset_lock(&connector->dev->mode_config.connection_mutex, &ctx);
+	if (!ret) {
+		if (funcs->detect_ctx)
+			ret = funcs->detect_ctx(connector, &ctx, force);
+		else if (connector->funcs->detect)
+			ret = connector->funcs->detect(connector, force);
+		else
+			ret = connector_status_connected;
+	}
+
+	if (ret == -EDEADLK) {
+		drm_modeset_backoff(&ctx);
+		goto retry;
+	}
+
+	if (WARN_ON(ret < 0))
+		ret = connector_status_unknown;
+
+	if (ret != connector->status)
+		connector->epoch_counter += 1;
+
+	drm_modeset_drop_locks(&ctx);
+	drm_modeset_acquire_fini(&ctx);
+
+	return ret;
+}
+
+/**
+ * drm_helper_probe_detect - probe connector status
+ * @connector: connector to probe
+ * @ctx: acquire_ctx, or NULL to let this function handle locking.
+ * @force: Whether destructive probe operations should be performed.
+ *
+ * This function calls the detect callbacks of the connector.
+ * This function returns &drm_connector_status, or
+ * if @ctx is set, it might also return -EDEADLK.
+ */
+int
+drm_helper_probe_detect(struct drm_connector *connector,
+			struct drm_modeset_acquire_ctx *ctx,
+			bool force)
+{
+	const struct drm_connector_helper_funcs *funcs = connector->helper_private;
+	struct drm_device *dev = connector->dev;
+	int ret;
+
+	if (!ctx)
+		return drm_helper_probe_detect_ctx(connector, force);
+
+	ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
+	if (ret)
+		return ret;
+
+	if (funcs->detect_ctx)
+		ret = funcs->detect_ctx(connector, ctx, force);
+	else if (connector->funcs->detect)
+		ret = connector->funcs->detect(connector, force);
+	else
+		ret = connector_status_connected;
+
+	if (ret != connector->status)
+		connector->epoch_counter += 1;
+
+	return ret;
+}
+EXPORT_SYMBOL(drm_helper_probe_detect);
+
+static int drm_helper_probe_get_modes(struct drm_connector *connector)
+{
+	const struct drm_connector_helper_funcs *connector_funcs =
+		connector->helper_private;
+	int count;
+
+	count = connector_funcs->get_modes(connector);
+
+	/*
+	 * Fallback for when DDC probe failed in drm_get_edid() and thus skipped
+	 * override/firmware EDID.
+	 */
+	if (count == 0 && connector->status == connector_status_connected)
+		count = drm_edid_override_connector_update(connector);
+
+	return count;
+}
+
+static int __drm_helper_update_and_validate(struct drm_connector *connector,
+					    uint32_t maxX, uint32_t maxY,
+					    struct drm_modeset_acquire_ctx *ctx)
+{
+	struct drm_device *dev = connector->dev;
+	struct drm_display_mode *mode;
+	int mode_flags = 0;
+	int ret;
+
+	drm_connector_list_update(connector);
+
+	if (connector->interlace_allowed)
+		mode_flags |= DRM_MODE_FLAG_INTERLACE;
+	if (connector->doublescan_allowed)
+		mode_flags |= DRM_MODE_FLAG_DBLSCAN;
+	if (connector->stereo_allowed)
+		mode_flags |= DRM_MODE_FLAG_3D_MASK;
+
+	list_for_each_entry(mode, &connector->modes, head) {
+		if (mode->status != MODE_OK)
+			continue;
+
+		mode->status = drm_mode_validate_driver(dev, mode);
+		if (mode->status != MODE_OK)
+			continue;
+
+		mode->status = drm_mode_validate_size(mode, maxX, maxY);
+		if (mode->status != MODE_OK)
+			continue;
+
+		mode->status = drm_mode_validate_flag(mode, mode_flags);
+		if (mode->status != MODE_OK)
+			continue;
+
+		ret = drm_mode_validate_pipeline(mode, connector, ctx,
+						 &mode->status);
+		if (ret) {
+			drm_dbg_kms(dev,
+				    "drm_mode_validate_pipeline failed: %d\n",
+				    ret);
+
+			if (drm_WARN_ON_ONCE(dev, ret != -EDEADLK))
+				mode->status = MODE_ERROR;
+			else
+				return -EDEADLK;
+		}
+
+		if (mode->status != MODE_OK)
+			continue;
+		mode->status = drm_mode_validate_ycbcr420(mode, connector);
+	}
+
+	return 0;
+}
+
+/**
+ * drm_helper_probe_single_connector_modes - get complete set of display modes
+ * @connector: connector to probe
+ * @maxX: max width for modes
+ * @maxY: max height for modes
+ *
+ * Based on the helper callbacks implemented by @connector in struct
+ * &drm_connector_helper_funcs try to detect all valid modes.  Modes will first
+ * be added to the connector's probed_modes list, then culled (based on validity
+ * and the @maxX, @maxY parameters) and put into the normal modes list.
+ *
+ * Intended to be used as a generic implementation of the
+ * &drm_connector_funcs.fill_modes() vfunc for drivers that use the CRTC helpers
+ * for output mode filtering and detection.
+ *
+ * The basic procedure is as follows
+ *
+ * 1. All modes currently on the connector's modes list are marked as stale
+ *
+ * 2. New modes are added to the connector's probed_modes list with
+ *    drm_mode_probed_add(). New modes start their life with status as OK.
+ *    Modes are added from a single source using the following priority order.
+ *
+ *    - &drm_connector_helper_funcs.get_modes vfunc
+ *    - if the connector status is connector_status_connected, standard
+ *      VESA DMT modes up to 1024x768 are automatically added
+ *      (drm_add_modes_noedid())
+ *
+ *    Finally modes specified via the kernel command line (video=...) are
+ *    added in addition to what the earlier probes produced
+ *    (drm_helper_probe_add_cmdline_mode()). These modes are generated
+ *    using the VESA GTF/CVT formulas.
+ *
+ * 3. Modes are moved from the probed_modes list to the modes list. Potential
+ *    duplicates are merged together (see drm_connector_list_update()).
+ *    After this step the probed_modes list will be empty again.
+ *
+ * 4. Any non-stale mode on the modes list then undergoes validation
+ *
+ *    - drm_mode_validate_basic() performs basic sanity checks
+ *    - drm_mode_validate_size() filters out modes larger than @maxX and @maxY
+ *      (if specified)
+ *    - drm_mode_validate_flag() checks the modes against basic connector
+ *      capabilities (interlace_allowed,doublescan_allowed,stereo_allowed)
+ *    - the optional &drm_connector_helper_funcs.mode_valid or
+ *      &drm_connector_helper_funcs.mode_valid_ctx helpers can perform driver
+ *      and/or sink specific checks
+ *    - the optional &drm_crtc_helper_funcs.mode_valid,
+ *      &drm_bridge_funcs.mode_valid and &drm_encoder_helper_funcs.mode_valid
+ *      helpers can perform driver and/or source specific checks which are also
+ *      enforced by the modeset/atomic helpers
+ *
+ * 5. Any mode whose status is not OK is pruned from the connector's modes list,
+ *    accompanied by a debug message indicating the reason for the mode's
+ *    rejection (see drm_mode_prune_invalid()).
+ *
+ * Returns:
+ * The number of modes found on @connector.
+ */
+int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
+					    uint32_t maxX, uint32_t maxY)
+{
+	struct drm_device *dev = connector->dev;
+	struct drm_display_mode *mode;
+	int count = 0, ret;
+	enum drm_connector_status old_status;
+	struct drm_modeset_acquire_ctx ctx;
+
+	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
+
+	drm_modeset_acquire_init(&ctx, 0);
+
+	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n", connector->base.id,
+			connector->name);
+
+retry:
+	ret = drm_modeset_lock(&dev->mode_config.connection_mutex, &ctx);
+	if (ret == -EDEADLK) {
+		drm_modeset_backoff(&ctx);
+		goto retry;
+	} else
+		WARN_ON(ret < 0);
+
+	/* set all old modes to the stale state */
+	list_for_each_entry(mode, &connector->modes, head)
+		mode->status = MODE_STALE;
+
+	old_status = connector->status;
+
+	if (connector->force) {
+		if (connector->force == DRM_FORCE_ON ||
+		    connector->force == DRM_FORCE_ON_DIGITAL)
+			connector->status = connector_status_connected;
+		else
+			connector->status = connector_status_disconnected;
+		if (connector->funcs->force)
+			connector->funcs->force(connector);
+	} else {
+		ret = drm_helper_probe_detect(connector, &ctx, true);
+
+		if (ret == -EDEADLK) {
+			drm_modeset_backoff(&ctx);
+			goto retry;
+		} else if (WARN(ret < 0, "Invalid return value %i for connector detection\n", ret))
+			ret = connector_status_unknown;
+
+		connector->status = ret;
+	}
+
+	/*
+	 * Normally either the driver's hpd code or the poll loop should
+	 * pick up any changes and fire the hotplug event. But if
+	 * userspace sneaks in a probe, we might miss a change. Hence
+	 * check here, and if anything changed start the hotplug code.
+	 */
+	if (old_status != connector->status) {
+		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] status updated from %s to %s\n",
+			      connector->base.id,
+			      connector->name,
+			      drm_get_connector_status_name(old_status),
+			      drm_get_connector_status_name(connector->status));
+
+		/*
+		 * The hotplug event code might call into the fb
+		 * helpers, and so expects that we do not hold any
+		 * locks. Fire up the poll struct instead, it will
+		 * disable itself again.
+		 */
+		dev->mode_config.delayed_event = true;
+		if (dev->mode_config.poll_enabled)
+			mod_delayed_work(system_wq,
+					 &dev->mode_config.output_poll_work,
+					 0);
+	}
+
+	/* Re-enable polling in case the global poll config changed. */
+	drm_kms_helper_poll_enable(dev);
+
+	if (connector->status == connector_status_disconnected) {
+		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] disconnected\n",
+			connector->base.id, connector->name);
+		drm_connector_update_edid_property(connector, NULL);
+		drm_mode_prune_invalid(dev, &connector->modes, false);
+		goto exit;
+	}
+
+	count = drm_helper_probe_get_modes(connector);
+
+	if (count == 0 && (connector->status == connector_status_connected ||
+			   connector->status == connector_status_unknown)) {
+		count = drm_add_modes_noedid(connector, 1024, 768);
+
+		/*
+		 * Section 4.2.2.6 (EDID Corruption Detection) of the DP 1.4a
+		 * Link CTS specifies that 640x480 (the official "failsafe"
+		 * mode) needs to be the default if there's no EDID.
+		 */
+		if (connector->connector_type == DRM_MODE_CONNECTOR_DisplayPort)
+			drm_set_preferred_mode(connector, 640, 480);
+	}
+	count += drm_helper_probe_add_cmdline_mode(connector);
+	if (count != 0) {
+		ret = __drm_helper_update_and_validate(connector, maxX, maxY, &ctx);
+		if (ret == -EDEADLK) {
+			drm_modeset_backoff(&ctx);
+			goto retry;
+		}
+	}
+
+	drm_mode_prune_invalid(dev, &connector->modes, true);
+
+	/*
+	 * Displayport spec section 5.2.1.2 ("Video Timing Format") says that
+	 * all detachable sinks shall support 640x480 @60Hz as a fail safe
+	 * mode. If all modes were pruned, perhaps because they need more
+	 * lanes or a higher pixel clock than available, at least try to add
+	 * in 640x480.
+	 */
+	if (list_empty(&connector->modes) &&
+	    connector->connector_type == DRM_MODE_CONNECTOR_DisplayPort) {
+		count = drm_add_modes_noedid(connector, 640, 480);
+		ret = __drm_helper_update_and_validate(connector, maxX, maxY, &ctx);
+		if (ret == -EDEADLK) {
+			drm_modeset_backoff(&ctx);
+			goto retry;
+		}
+		drm_mode_prune_invalid(dev, &connector->modes, true);
+	}
+
+exit:
+	drm_modeset_drop_locks(&ctx);
+	drm_modeset_acquire_fini(&ctx);
+
+	if (list_empty(&connector->modes))
+		return 0;
+
+	drm_mode_sort(&connector->modes);
+
+	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] probed modes :\n", connector->base.id,
+			connector->name);
+	list_for_each_entry(mode, &connector->modes, head) {
+		drm_mode_set_crtcinfo(mode, CRTC_INTERLACE_HALVE_V);
+		drm_mode_debug_printmodeline(mode);
+	}
+
+	return count;
+}
+EXPORT_SYMBOL(drm_helper_probe_single_connector_modes);
+
+/**
+ * drm_kms_helper_hotplug_event - fire off KMS hotplug events
+ * @dev: drm_device whose connector state changed
+ *
+ * This function fires off the uevent for userspace and also calls the
+ * output_poll_changed function, which is most commonly used to inform the fbdev
+ * emulation code and allow it to update the fbcon output configuration.
+ *
+ * Drivers should call this from their hotplug handling code when a change is
+ * detected. Note that this function does not do any output detection of its
+ * own, like drm_helper_hpd_irq_event() does - this is assumed to be done by the
+ * driver already.
+ *
+ * This function must be called from process context with no mode
+ * setting locks held.
+ *
+ * If only a single connector has changed, consider calling
+ * drm_kms_helper_connector_hotplug_event() instead.
+ */
+void drm_kms_helper_hotplug_event(struct drm_device *dev)
+{
+	/* send a uevent + call fbdev */
+	drm_sysfs_hotplug_event(dev);
+	if (dev->mode_config.funcs->output_poll_changed)
+		dev->mode_config.funcs->output_poll_changed(dev);
+
+	drm_client_dev_hotplug(dev);
+}
+EXPORT_SYMBOL(drm_kms_helper_hotplug_event);
+
+/**
+ * drm_kms_helper_connector_hotplug_event - fire off a KMS connector hotplug event
+ * @connector: drm_connector which has changed
+ *
+ * This is the same as drm_kms_helper_hotplug_event(), except it fires a more
+ * fine-grained uevent for a single connector.
+ */
+void drm_kms_helper_connector_hotplug_event(struct drm_connector *connector)
+{
+	struct drm_device *dev = connector->dev;
+
+	/* send a uevent + call fbdev */
+	drm_sysfs_connector_hotplug_event(connector);
+	if (dev->mode_config.funcs->output_poll_changed)
+		dev->mode_config.funcs->output_poll_changed(dev);
+
+	drm_client_dev_hotplug(dev);
+}
+EXPORT_SYMBOL(drm_kms_helper_connector_hotplug_event);
+
+static void output_poll_execute(struct work_struct *work)
+{
+	struct delayed_work *delayed_work = to_delayed_work(work);
+	struct drm_device *dev = container_of(delayed_work, struct drm_device, mode_config.output_poll_work);
+	struct drm_connector *connector;
+	struct drm_connector_list_iter conn_iter;
+	enum drm_connector_status old_status;
+	bool repoll = false, changed;
+	u64 old_epoch_counter;
+
+	if (!dev->mode_config.poll_enabled)
+		return;
+
+	/* Pick up any changes detected by the probe functions. */
+	changed = dev->mode_config.delayed_event;
+	dev->mode_config.delayed_event = false;
+
+	if (!drm_kms_helper_poll && dev->mode_config.poll_running) {
+		drm_kms_helper_disable_hpd(dev);
+		dev->mode_config.poll_running = false;
+		goto out;
+	}
+
+	if (!mutex_trylock(&dev->mode_config.mutex)) {
+		repoll = true;
+		goto out;
+	}
+
+	drm_connector_list_iter_begin(dev, &conn_iter);
+	drm_for_each_connector_iter(connector, &conn_iter) {
+		/* Ignore forced connectors. */
+		if (connector->force)
+			continue;
+
+		/* Ignore HPD capable connectors and connectors where we don't
+		 * want any hotplug detection at all for polling. */
+		if (!connector->polled || connector->polled == DRM_CONNECTOR_POLL_HPD)
+			continue;
+
+		old_status = connector->status;
+		/* if we are connected and don't want to poll for disconnect
+		   skip it */
+		if (old_status == connector_status_connected &&
+		    !(connector->polled & DRM_CONNECTOR_POLL_DISCONNECT))
+			continue;
+
+		repoll = true;
+
+		old_epoch_counter = connector->epoch_counter;
+		connector->status = drm_helper_probe_detect(connector, NULL, false);
+		if (old_epoch_counter != connector->epoch_counter) {
+			const char *old, *new;
+
+			/*
+			 * The poll work sets force=false when calling detect so
+			 * that drivers can avoid to do disruptive tests (e.g.
+			 * when load detect cycles could cause flickering on
+			 * other, running displays). This bears the risk that we
+			 * flip-flop between unknown here in the poll work and
+			 * the real state when userspace forces a full detect
+			 * call after receiving a hotplug event due to this
+			 * change.
+			 *
+			 * Hence clamp an unknown detect status to the old
+			 * value.
+			 */
+			if (connector->status == connector_status_unknown) {
+				connector->status = old_status;
+				continue;
+			}
+
+			old = drm_get_connector_status_name(old_status);
+			new = drm_get_connector_status_name(connector->status);
+
+			DRM_DEBUG_KMS("[CONNECTOR:%d:%s] "
+				      "status updated from %s to %s\n",
+				      connector->base.id,
+				      connector->name,
+				      old, new);
+			DRM_DEBUG_KMS("[CONNECTOR:%d:%s] epoch counter %llu -> %llu\n",
+				      connector->base.id, connector->name,
+				      old_epoch_counter, connector->epoch_counter);
+
+			changed = true;
+		}
+	}
+	drm_connector_list_iter_end(&conn_iter);
+
+	mutex_unlock(&dev->mode_config.mutex);
+
+out:
+	if (changed)
+		drm_kms_helper_hotplug_event(dev);
+
+	if (repoll)
+		schedule_delayed_work(delayed_work, DRM_OUTPUT_POLL_PERIOD);
+}
+
+/**
+ * drm_kms_helper_is_poll_worker - is %current task an output poll worker?
+ *
+ * Determine if %current task is an output poll worker.  This can be used
+ * to select distinct code paths for output polling versus other contexts.
+ *
+ * One use case is to avoid a deadlock between the output poll worker and
+ * the autosuspend worker wherein the latter waits for polling to finish
+ * upon calling drm_kms_helper_poll_disable(), while the former waits for
+ * runtime suspend to finish upon calling pm_runtime_get_sync() in a
+ * connector ->detect hook.
+ */
+bool drm_kms_helper_is_poll_worker(void)
+{
+	struct work_struct *work = current_work();
+
+	return work && work->func == output_poll_execute;
+}
+EXPORT_SYMBOL(drm_kms_helper_is_poll_worker);
+
+/**
+ * drm_kms_helper_poll_disable - disable output polling
+ * @dev: drm_device
+ *
+ * This function disables the output polling work.
+ *
+ * Drivers can call this helper from their device suspend implementation. It is
+ * not an error to call this even when output polling isn't enabled or already
+ * disabled. Polling is re-enabled by calling drm_kms_helper_poll_enable().
+ *
+ * Note that calls to enable and disable polling must be strictly ordered, which
+ * is automatically the case when they're only call from suspend/resume
+ * callbacks.
+ */
+void drm_kms_helper_poll_disable(struct drm_device *dev)
+{
+	if (dev->mode_config.poll_running)
+		drm_kms_helper_disable_hpd(dev);
+
+	cancel_delayed_work_sync(&dev->mode_config.output_poll_work);
+
+	dev->mode_config.poll_running = false;
+}
+EXPORT_SYMBOL(drm_kms_helper_poll_disable);
+
+/**
+ * drm_kms_helper_poll_init - initialize and enable output polling
+ * @dev: drm_device
+ *
+ * This function initializes and then also enables output polling support for
+ * @dev. Drivers which do not have reliable hotplug support in hardware can use
+ * this helper infrastructure to regularly poll such connectors for changes in
+ * their connection state.
+ *
+ * Drivers can control which connectors are polled by setting the
+ * DRM_CONNECTOR_POLL_CONNECT and DRM_CONNECTOR_POLL_DISCONNECT flags. On
+ * connectors where probing live outputs can result in visual distortion drivers
+ * should not set the DRM_CONNECTOR_POLL_DISCONNECT flag to avoid this.
+ * Connectors which have no flag or only DRM_CONNECTOR_POLL_HPD set are
+ * completely ignored by the polling logic.
+ *
+ * Note that a connector can be both polled and probed from the hotplug handler,
+ * in case the hotplug interrupt is known to be unreliable.
+ */
+void drm_kms_helper_poll_init(struct drm_device *dev)
+{
+	INIT_DELAYED_WORK(&dev->mode_config.output_poll_work, output_poll_execute);
+	dev->mode_config.poll_enabled = true;
+
+	drm_kms_helper_poll_enable(dev);
+}
+EXPORT_SYMBOL(drm_kms_helper_poll_init);
+
+/**
+ * drm_kms_helper_poll_fini - disable output polling and clean it up
+ * @dev: drm_device
+ */
+void drm_kms_helper_poll_fini(struct drm_device *dev)
+{
+	if (!dev->mode_config.poll_enabled)
+		return;
+
+	drm_kms_helper_poll_disable(dev);
+
+	dev->mode_config.poll_enabled = false;
+}
+EXPORT_SYMBOL(drm_kms_helper_poll_fini);
+
+static bool check_connector_changed(struct drm_connector *connector)
+{
+	struct drm_device *dev = connector->dev;
+	enum drm_connector_status old_status;
+	u64 old_epoch_counter;
+
+	/* Only handle HPD capable connectors. */
+	drm_WARN_ON(dev, !(connector->polled & DRM_CONNECTOR_POLL_HPD));
+
+	drm_WARN_ON(dev, !mutex_is_locked(&dev->mode_config.mutex));
+
+	old_status = connector->status;
+	old_epoch_counter = connector->epoch_counter;
+	connector->status = drm_helper_probe_detect(connector, NULL, false);
+
+	if (old_epoch_counter == connector->epoch_counter) {
+		drm_dbg_kms(dev, "[CONNECTOR:%d:%s] Same epoch counter %llu\n",
+			    connector->base.id,
+			    connector->name,
+			    connector->epoch_counter);
+
+		return false;
+	}
+
+	drm_dbg_kms(dev, "[CONNECTOR:%d:%s] status updated from %s to %s\n",
+		    connector->base.id,
+		    connector->name,
+		    drm_get_connector_status_name(old_status),
+		    drm_get_connector_status_name(connector->status));
+
+	drm_dbg_kms(dev, "[CONNECTOR:%d:%s] Changed epoch counter %llu => %llu\n",
+		    connector->base.id,
+		    connector->name,
+		    old_epoch_counter,
+		    connector->epoch_counter);
+
+	return true;
+}
+
+/**
+ * drm_connector_helper_hpd_irq_event - hotplug processing
+ * @connector: drm_connector
+ *
+ * Drivers can use this helper function to run a detect cycle on a connector
+ * which has the DRM_CONNECTOR_POLL_HPD flag set in its &polled member.
+ *
+ * This helper function is useful for drivers which can track hotplug
+ * interrupts for a single connector. Drivers that want to send a
+ * hotplug event for all connectors or can't track hotplug interrupts
+ * per connector need to use drm_helper_hpd_irq_event().
+ *
+ * This function must be called from process context with no mode
+ * setting locks held.
+ *
+ * Note that a connector can be both polled and probed from the hotplug
+ * handler, in case the hotplug interrupt is known to be unreliable.
+ *
+ * Returns:
+ * A boolean indicating whether the connector status changed or not
+ */
+bool drm_connector_helper_hpd_irq_event(struct drm_connector *connector)
+{
+	struct drm_device *dev = connector->dev;
+	bool changed;
+
+	mutex_lock(&dev->mode_config.mutex);
+	changed = check_connector_changed(connector);
+	mutex_unlock(&dev->mode_config.mutex);
+
+	if (changed) {
+		drm_kms_helper_connector_hotplug_event(connector);
+		drm_dbg_kms(dev, "[CONNECTOR:%d:%s] Sent hotplug event\n",
+			    connector->base.id,
+			    connector->name);
+	}
+
+	return changed;
+}
+EXPORT_SYMBOL(drm_connector_helper_hpd_irq_event);
+
+/**
+ * drm_helper_hpd_irq_event - hotplug processing
+ * @dev: drm_device
+ *
+ * Drivers can use this helper function to run a detect cycle on all connectors
+ * which have the DRM_CONNECTOR_POLL_HPD flag set in their &polled member. All
+ * other connectors are ignored, which is useful to avoid reprobing fixed
+ * panels.
+ *
+ * This helper function is useful for drivers which can't or don't track hotplug
+ * interrupts for each connector.
+ *
+ * Drivers which support hotplug interrupts for each connector individually and
+ * which have a more fine-grained detect logic can use
+ * drm_connector_helper_hpd_irq_event(). Alternatively, they should bypass this
+ * code and directly call drm_kms_helper_hotplug_event() in case the connector
+ * state changed.
+ *
+ * This function must be called from process context with no mode
+ * setting locks held.
+ *
+ * Note that a connector can be both polled and probed from the hotplug handler,
+ * in case the hotplug interrupt is known to be unreliable.
+ *
+ * Returns:
+ * A boolean indicating whether the connector status changed or not
+ */
+bool drm_helper_hpd_irq_event(struct drm_device *dev)
+{
+	struct drm_connector *connector, *first_changed_connector = NULL;
+	struct drm_connector_list_iter conn_iter;
+	int changed = 0;
+
+	if (!dev->mode_config.poll_enabled)
+		return false;
+
+	mutex_lock(&dev->mode_config.mutex);
+	drm_connector_list_iter_begin(dev, &conn_iter);
+	drm_for_each_connector_iter(connector, &conn_iter) {
+		/* Only handle HPD capable connectors. */
+		if (!(connector->polled & DRM_CONNECTOR_POLL_HPD))
+			continue;
+
+		if (check_connector_changed(connector)) {
+			if (!first_changed_connector) {
+				drm_connector_get(connector);
+				first_changed_connector = connector;
+			}
+
+			changed++;
+		}
+	}
+	drm_connector_list_iter_end(&conn_iter);
+	mutex_unlock(&dev->mode_config.mutex);
+
+	if (changed == 1)
+		drm_kms_helper_connector_hotplug_event(first_changed_connector);
+	else if (changed > 0)
+		drm_kms_helper_hotplug_event(dev);
+
+	if (first_changed_connector)
+		drm_connector_put(first_changed_connector);
+
+	return changed;
+}
+EXPORT_SYMBOL(drm_helper_hpd_irq_event);
+
+/**
+ * drm_crtc_helper_mode_valid_fixed - Validates a display mode
+ * @crtc: the crtc
+ * @mode: the mode to validate
+ * @fixed_mode: the display hardware's mode
+ *
+ * Returns:
+ * MODE_OK on success, or another mode-status code otherwise.
+ */
+enum drm_mode_status drm_crtc_helper_mode_valid_fixed(struct drm_crtc *crtc,
+						      const struct drm_display_mode *mode,
+						      const struct drm_display_mode *fixed_mode)
+{
+	if (mode->hdisplay != fixed_mode->hdisplay && mode->vdisplay != fixed_mode->vdisplay)
+		return MODE_ONE_SIZE;
+	else if (mode->hdisplay != fixed_mode->hdisplay)
+		return MODE_ONE_WIDTH;
+	else if (mode->vdisplay != fixed_mode->vdisplay)
+		return MODE_ONE_HEIGHT;
+
+	return MODE_OK;
+}
+EXPORT_SYMBOL(drm_crtc_helper_mode_valid_fixed);
+
+/**
+ * drm_connector_helper_get_modes_from_ddc - Updates the connector's EDID
+ *                                           property from the connector's
+ *                                           DDC channel
+ * @connector: The connector
+ *
+ * Returns:
+ * The number of detected display modes.
+ *
+ * Uses a connector's DDC channel to retrieve EDID data and update the
+ * connector's EDID property and display modes. Drivers can use this
+ * function to implement struct &drm_connector_helper_funcs.get_modes
+ * for connectors with a DDC channel.
+ */
+int drm_connector_helper_get_modes_from_ddc(struct drm_connector *connector)
+{
+	struct edid *edid;
+	int count = 0;
+
+	if (!connector->ddc)
+		return 0;
+
+	edid = drm_get_edid(connector, connector->ddc);
+
+	// clears property if EDID is NULL
+	drm_connector_update_edid_property(connector, edid);
+
+	if (edid) {
+		count = drm_add_edid_modes(connector, edid);
+		kfree(edid);
+	}
+
+	return count;
+}
+EXPORT_SYMBOL(drm_connector_helper_get_modes_from_ddc);
+
+/**
+ * drm_connector_helper_get_modes_fixed - Duplicates a display mode for a connector
+ * @connector: the connector
+ * @fixed_mode: the display hardware's mode
+ *
+ * This function duplicates a display modes for a connector. Drivers for hardware
+ * that only supports a single fixed mode can use this function in their connector's
+ * get_modes helper.
+ *
+ * Returns:
+ * The number of created modes.
+ */
+int drm_connector_helper_get_modes_fixed(struct drm_connector *connector,
+					 const struct drm_display_mode *fixed_mode)
+{
+	struct drm_device *dev = connector->dev;
+	struct drm_display_mode *mode;
+
+	mode = drm_mode_duplicate(dev, fixed_mode);
+	if (!mode) {
+		drm_err(dev, "Failed to duplicate mode " DRM_MODE_FMT "\n",
+			DRM_MODE_ARG(fixed_mode));
+		return 0;
+	}
+
+	if (mode->name[0] == '\0')
+		drm_mode_set_name(mode);
+
+	mode->type |= DRM_MODE_TYPE_PREFERRED;
+	drm_mode_probed_add(connector, mode);
+
+	if (mode->width_mm)
+		connector->display_info.width_mm = mode->width_mm;
+	if (mode->height_mm)
+		connector->display_info.height_mm = mode->height_mm;
+
+	return 1;
+}
+EXPORT_SYMBOL(drm_connector_helper_get_modes_fixed);
+
+/**
+ * drm_connector_helper_get_modes - Read EDID and update connector.
+ * @connector: The connector
+ *
+ * Read the EDID using drm_edid_read() (which requires that connector->ddc is
+ * set), and update the connector using the EDID.
+ *
+ * This can be used as the "default" connector helper .get_modes() hook if the
+ * driver does not need any special processing. This is sets the example what
+ * custom .get_modes() hooks should do regarding EDID read and connector update.
+ *
+ * Returns: Number of modes.
+ */
+int drm_connector_helper_get_modes(struct drm_connector *connector)
+{
+	const struct drm_edid *drm_edid;
+	int count;
+
+	drm_edid = drm_edid_read(connector);
+
+	/*
+	 * Unconditionally update the connector. If the EDID was read
+	 * successfully, fill in the connector information derived from the
+	 * EDID. Otherwise, if the EDID is NULL, clear the connector
+	 * information.
+	 */
+	drm_edid_connector_update(connector, drm_edid);
+
+	count = drm_edid_connector_add_modes(connector);
+
+	drm_edid_free(drm_edid);
+
+	return count;
+}
+EXPORT_SYMBOL(drm_connector_helper_get_modes);
+
+/**
+ * drm_connector_helper_tv_get_modes - Fills the modes availables to a TV connector
+ * @connector: The connector
+ *
+ * Fills the available modes for a TV connector based on the supported
+ * TV modes, and the default mode expressed by the kernel command line.
+ *
+ * This can be used as the default TV connector helper .get_modes() hook
+ * if the driver does not need any special processing.
+ *
+ * Returns:
+ * The number of modes added to the connector.
+ */
+int drm_connector_helper_tv_get_modes(struct drm_connector *connector)
+{
+	struct drm_device *dev = connector->dev;
+	struct drm_property *tv_mode_property =
+		dev->mode_config.tv_mode_property;
+	struct drm_cmdline_mode *cmdline = &connector->cmdline_mode;
+	unsigned int ntsc_modes = BIT(DRM_MODE_TV_MODE_NTSC) |
+		BIT(DRM_MODE_TV_MODE_NTSC_443) |
+		BIT(DRM_MODE_TV_MODE_NTSC_J) |
+		BIT(DRM_MODE_TV_MODE_PAL_M);
+	unsigned int pal_modes = BIT(DRM_MODE_TV_MODE_PAL) |
+		BIT(DRM_MODE_TV_MODE_PAL_N) |
+		BIT(DRM_MODE_TV_MODE_SECAM);
+	unsigned int tv_modes[2] = { UINT_MAX, UINT_MAX };
+	unsigned int i, supported_tv_modes = 0;
+
+	if (!tv_mode_property)
+		return 0;
+
+	for (i = 0; i < tv_mode_property->num_values; i++)
+		supported_tv_modes |= BIT(tv_mode_property->values[i]);
+
+	if ((supported_tv_modes & ntsc_modes) &&
+	    (supported_tv_modes & pal_modes)) {
+		uint64_t default_mode;
+
+		if (drm_object_property_get_default_value(&connector->base,
+							  tv_mode_property,
+							  &default_mode))
+			return 0;
+
+		if (cmdline->tv_mode_specified)
+			default_mode = cmdline->tv_mode;
+
+		if (BIT(default_mode) & ntsc_modes) {
+			tv_modes[0] = DRM_MODE_TV_MODE_NTSC;
+			tv_modes[1] = DRM_MODE_TV_MODE_PAL;
+		} else {
+			tv_modes[0] = DRM_MODE_TV_MODE_PAL;
+			tv_modes[1] = DRM_MODE_TV_MODE_NTSC;
+		}
+	} else if (supported_tv_modes & ntsc_modes) {
+		tv_modes[0] = DRM_MODE_TV_MODE_NTSC;
+	} else if (supported_tv_modes & pal_modes) {
+		tv_modes[0] = DRM_MODE_TV_MODE_PAL;
+	} else {
+		return 0;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(tv_modes); i++) {
+		struct drm_display_mode *mode;
+
+		if (tv_modes[i] == DRM_MODE_TV_MODE_NTSC)
+			mode = drm_mode_analog_ntsc_480i(dev);
+		else if (tv_modes[i] == DRM_MODE_TV_MODE_PAL)
+			mode = drm_mode_analog_pal_576i(dev);
+		else
+			break;
+		if (!mode)
+			return i;
+		if (!i)
+			mode->type |= DRM_MODE_TYPE_PREFERRED;
+		drm_mode_probed_add(connector, mode);
+	}
+
+	return i;
+}
+EXPORT_SYMBOL(drm_connector_helper_tv_get_modes);