Adding upstream version 6.6.15.upstream/6.6.15

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

1 files changed, 549 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
new file mode 100644
index 000000000..95cc52518
--- /dev/null
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
@@ -0,0 +1,549 @@
+/*
+ * Copyright © 2015 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ */
+
+/*
+ * Laptops with Intel GPUs which have panels that support controlling the
+ * backlight through DP AUX can actually use two different interfaces: Intel's
+ * proprietary DP AUX backlight interface, and the standard VESA backlight
+ * interface. Unfortunately, at the time of writing this a lot of laptops will
+ * advertise support for the standard VESA backlight interface when they
+ * don't properly support it. However, on these systems the Intel backlight
+ * interface generally does work properly. Additionally, these systems will
+ * usually just indicate that they use PWM backlight controls in their VBIOS
+ * for some reason.
+ */
+
+#include "i915_drv.h"
+#include "intel_backlight.h"
+#include "intel_display_types.h"
+#include "intel_dp.h"
+#include "intel_dp_aux_backlight.h"
+
+/* TODO:
+ * Implement HDR, right now we just implement the bare minimum to bring us back into SDR mode so we
+ * can make people's backlights work in the mean time
+ */
+
+/*
+ * DP AUX registers for Intel's proprietary HDR backlight interface. We define
+ * them here since we'll likely be the only driver to ever use these.
+ */
+#define INTEL_EDP_HDR_TCON_CAP0                                        0x340
+
+#define INTEL_EDP_HDR_TCON_CAP1                                        0x341
+# define INTEL_EDP_HDR_TCON_2084_DECODE_CAP                           BIT(0)
+# define INTEL_EDP_HDR_TCON_2020_GAMUT_CAP                            BIT(1)
+# define INTEL_EDP_HDR_TCON_TONE_MAPPING_CAP                          BIT(2)
+# define INTEL_EDP_HDR_TCON_SEGMENTED_BACKLIGHT_CAP                   BIT(3)
+# define INTEL_EDP_HDR_TCON_BRIGHTNESS_NITS_CAP                       BIT(4)
+# define INTEL_EDP_HDR_TCON_OPTIMIZATION_CAP                          BIT(5)
+# define INTEL_EDP_HDR_TCON_SDP_COLORIMETRY_CAP                       BIT(6)
+# define INTEL_EDP_HDR_TCON_SRGB_TO_PANEL_GAMUT_CONVERSION_CAP        BIT(7)
+
+#define INTEL_EDP_HDR_TCON_CAP2                                        0x342
+# define INTEL_EDP_SDR_TCON_BRIGHTNESS_AUX_CAP                        BIT(0)
+
+#define INTEL_EDP_HDR_TCON_CAP3                                        0x343
+
+#define INTEL_EDP_HDR_GETSET_CTRL_PARAMS                               0x344
+# define INTEL_EDP_HDR_TCON_2084_DECODE_ENABLE                        BIT(0)
+# define INTEL_EDP_HDR_TCON_2020_GAMUT_ENABLE                         BIT(1)
+# define INTEL_EDP_HDR_TCON_TONE_MAPPING_ENABLE                       BIT(2) /* Pre-TGL+ */
+# define INTEL_EDP_HDR_TCON_SEGMENTED_BACKLIGHT_ENABLE                BIT(3)
+# define INTEL_EDP_HDR_TCON_BRIGHTNESS_AUX_ENABLE                     BIT(4)
+# define INTEL_EDP_HDR_TCON_SRGB_TO_PANEL_GAMUT_ENABLE                BIT(5)
+/* Bit 6 is reserved */
+# define INTEL_EDP_HDR_TCON_SDP_COLORIMETRY_ENABLE                    BIT(7)
+
+#define INTEL_EDP_HDR_CONTENT_LUMINANCE                                0x346 /* Pre-TGL+ */
+#define INTEL_EDP_HDR_PANEL_LUMINANCE_OVERRIDE                         0x34A
+#define INTEL_EDP_SDR_LUMINANCE_LEVEL                                  0x352
+#define INTEL_EDP_BRIGHTNESS_NITS_LSB                                  0x354
+#define INTEL_EDP_BRIGHTNESS_NITS_MSB                                  0x355
+#define INTEL_EDP_BRIGHTNESS_DELAY_FRAMES                              0x356
+#define INTEL_EDP_BRIGHTNESS_PER_FRAME_STEPS                           0x357
+
+#define INTEL_EDP_BRIGHTNESS_OPTIMIZATION_0                            0x358
+# define INTEL_EDP_TCON_USAGE_MASK                             GENMASK(0, 3)
+# define INTEL_EDP_TCON_USAGE_UNKNOWN                                    0x0
+# define INTEL_EDP_TCON_USAGE_DESKTOP                                    0x1
+# define INTEL_EDP_TCON_USAGE_FULL_SCREEN_MEDIA                          0x2
+# define INTEL_EDP_TCON_USAGE_FULL_SCREEN_GAMING                         0x3
+# define INTEL_EDP_TCON_POWER_MASK                                    BIT(4)
+# define INTEL_EDP_TCON_POWER_DC                                    (0 << 4)
+# define INTEL_EDP_TCON_POWER_AC                                    (1 << 4)
+# define INTEL_EDP_TCON_OPTIMIZATION_STRENGTH_MASK             GENMASK(5, 7)
+
+#define INTEL_EDP_BRIGHTNESS_OPTIMIZATION_1                            0x359
+
+enum intel_dp_aux_backlight_modparam {
+	INTEL_DP_AUX_BACKLIGHT_AUTO = -1,
+	INTEL_DP_AUX_BACKLIGHT_OFF = 0,
+	INTEL_DP_AUX_BACKLIGHT_ON = 1,
+	INTEL_DP_AUX_BACKLIGHT_FORCE_VESA = 2,
+	INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL = 3,
+};
+
+static bool is_intel_tcon_cap(const u8 tcon_cap[4])
+{
+	return tcon_cap[0] >= 1;
+}
+
+/* Intel EDP backlight callbacks */
+static bool
+intel_dp_aux_supports_hdr_backlight(struct intel_connector *connector)
+{
+	struct drm_i915_private *i915 = to_i915(connector->base.dev);
+	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
+	struct drm_dp_aux *aux = &intel_dp->aux;
+	struct intel_panel *panel = &connector->panel;
+	int ret;
+	u8 tcon_cap[4];
+
+	intel_dp_wait_source_oui(intel_dp);
+
+	ret = drm_dp_dpcd_read(aux, INTEL_EDP_HDR_TCON_CAP0, tcon_cap, sizeof(tcon_cap));
+	if (ret != sizeof(tcon_cap))
+		return false;
+
+	if (!(tcon_cap[1] & INTEL_EDP_HDR_TCON_BRIGHTNESS_NITS_CAP))
+		return false;
+
+	drm_dbg_kms(&i915->drm, "[CONNECTOR:%d:%s] Detected %s HDR backlight interface version %d\n",
+		    connector->base.base.id, connector->base.name,
+		    is_intel_tcon_cap(tcon_cap) ? "Intel" : "unsupported", tcon_cap[0]);
+
+	if (!is_intel_tcon_cap(tcon_cap))
+		return false;
+
+	/*
+	 * If we don't have HDR static metadata there is no way to
+	 * runtime detect used range for nits based control. For now
+	 * do not use Intel proprietary eDP backlight control if we
+	 * don't have this data in panel EDID. In case we find panel
+	 * which supports only nits based control, but doesn't provide
+	 * HDR static metadata we need to start maintaining table of
+	 * ranges for such panels.
+	 */
+	if (i915->params.enable_dpcd_backlight != INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL &&
+	    !(connector->base.hdr_sink_metadata.hdmi_type1.metadata_type &
+	      BIT(HDMI_STATIC_METADATA_TYPE1))) {
+		drm_info(&i915->drm,
+			 "[CONNECTOR:%d:%s] Panel is missing HDR static metadata. Possible support for Intel HDR backlight interface is not used. If your backlight controls don't work try booting with i915.enable_dpcd_backlight=%d. needs this, please file a _new_ bug report on drm/i915, see " FDO_BUG_URL " for details.\n",
+			 connector->base.base.id, connector->base.name,
+			 INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL);
+		return false;
+	}
+
+	panel->backlight.edp.intel.sdr_uses_aux =
+		tcon_cap[2] & INTEL_EDP_SDR_TCON_BRIGHTNESS_AUX_CAP;
+
+	return true;
+}
+
+static u32
+intel_dp_aux_hdr_get_backlight(struct intel_connector *connector, enum pipe pipe)
+{
+	struct drm_i915_private *i915 = to_i915(connector->base.dev);
+	struct intel_panel *panel = &connector->panel;
+	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
+	u8 tmp;
+	u8 buf[2] = { 0 };
+
+	if (drm_dp_dpcd_readb(&intel_dp->aux, INTEL_EDP_HDR_GETSET_CTRL_PARAMS, &tmp) != 1) {
+		drm_err(&i915->drm, "[CONNECTOR:%d:%s] Failed to read current backlight mode from DPCD\n",
+			connector->base.base.id, connector->base.name);
+		return 0;
+	}
+
+	if (!(tmp & INTEL_EDP_HDR_TCON_BRIGHTNESS_AUX_ENABLE)) {
+		if (!panel->backlight.edp.intel.sdr_uses_aux) {
+			u32 pwm_level = panel->backlight.pwm_funcs->get(connector, pipe);
+
+			return intel_backlight_level_from_pwm(connector, pwm_level);
+		}
+
+		/* Assume 100% brightness if backlight controls aren't enabled yet */
+		return panel->backlight.max;
+	}
+
+	if (drm_dp_dpcd_read(&intel_dp->aux, INTEL_EDP_BRIGHTNESS_NITS_LSB, buf,
+			     sizeof(buf)) != sizeof(buf)) {
+		drm_err(&i915->drm, "[CONNECTOR:%d:%s] Failed to read brightness from DPCD\n",
+			connector->base.base.id, connector->base.name);
+		return 0;
+	}
+
+	return (buf[1] << 8 | buf[0]);
+}
+
+static void
+intel_dp_aux_hdr_set_aux_backlight(const struct drm_connector_state *conn_state, u32 level)
+{
+	struct intel_connector *connector = to_intel_connector(conn_state->connector);
+	struct drm_device *dev = connector->base.dev;
+	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
+	u8 buf[4] = { 0 };
+
+	buf[0] = level & 0xFF;
+	buf[1] = (level & 0xFF00) >> 8;
+
+	if (drm_dp_dpcd_write(&intel_dp->aux, INTEL_EDP_BRIGHTNESS_NITS_LSB, buf,
+			      sizeof(buf)) != sizeof(buf))
+		drm_err(dev, "[CONNECTOR:%d:%s] Failed to write brightness level to DPCD\n",
+			connector->base.base.id, connector->base.name);
+}
+
+static void
+intel_dp_aux_hdr_set_backlight(const struct drm_connector_state *conn_state, u32 level)
+{
+	struct intel_connector *connector = to_intel_connector(conn_state->connector);
+	struct intel_panel *panel = &connector->panel;
+
+	if (panel->backlight.edp.intel.sdr_uses_aux) {
+		intel_dp_aux_hdr_set_aux_backlight(conn_state, level);
+	} else {
+		const u32 pwm_level = intel_backlight_level_to_pwm(connector, level);
+
+		intel_backlight_set_pwm_level(conn_state, pwm_level);
+	}
+}
+
+static void
+intel_dp_aux_hdr_enable_backlight(const struct intel_crtc_state *crtc_state,
+				  const struct drm_connector_state *conn_state, u32 level)
+{
+	struct intel_connector *connector = to_intel_connector(conn_state->connector);
+	struct intel_panel *panel = &connector->panel;
+	struct drm_i915_private *i915 = to_i915(connector->base.dev);
+	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
+	int ret;
+	u8 old_ctrl, ctrl;
+
+	intel_dp_wait_source_oui(intel_dp);
+
+	ret = drm_dp_dpcd_readb(&intel_dp->aux, INTEL_EDP_HDR_GETSET_CTRL_PARAMS, &old_ctrl);
+	if (ret != 1) {
+		drm_err(&i915->drm, "[CONNECTOR:%d:%s] Failed to read current backlight control mode: %d\n",
+			connector->base.base.id, connector->base.name, ret);
+		return;
+	}
+
+	ctrl = old_ctrl;
+	if (panel->backlight.edp.intel.sdr_uses_aux) {
+		ctrl |= INTEL_EDP_HDR_TCON_BRIGHTNESS_AUX_ENABLE;
+		intel_dp_aux_hdr_set_aux_backlight(conn_state, level);
+	} else {
+		u32 pwm_level = intel_backlight_level_to_pwm(connector, level);
+
+		panel->backlight.pwm_funcs->enable(crtc_state, conn_state, pwm_level);
+
+		ctrl &= ~INTEL_EDP_HDR_TCON_BRIGHTNESS_AUX_ENABLE;
+	}
+
+	if (ctrl != old_ctrl &&
+	    drm_dp_dpcd_writeb(&intel_dp->aux, INTEL_EDP_HDR_GETSET_CTRL_PARAMS, ctrl) != 1)
+		drm_err(&i915->drm, "[CONNECTOR:%d:%s] Failed to configure DPCD brightness controls\n",
+			connector->base.base.id, connector->base.name);
+}
+
+static void
+intel_dp_aux_hdr_disable_backlight(const struct drm_connector_state *conn_state, u32 level)
+{
+	struct intel_connector *connector = to_intel_connector(conn_state->connector);
+	struct intel_panel *panel = &connector->panel;
+
+	/* Nothing to do for AUX based backlight controls */
+	if (panel->backlight.edp.intel.sdr_uses_aux)
+		return;
+
+	/* Note we want the actual pwm_level to be 0, regardless of pwm_min */
+	panel->backlight.pwm_funcs->disable(conn_state, intel_backlight_invert_pwm_level(connector, 0));
+}
+
+static const char *dpcd_vs_pwm_str(bool aux)
+{
+	return aux ? "DPCD" : "PWM";
+}
+
+static int
+intel_dp_aux_hdr_setup_backlight(struct intel_connector *connector, enum pipe pipe)
+{
+	struct drm_i915_private *i915 = to_i915(connector->base.dev);
+	struct intel_panel *panel = &connector->panel;
+	struct drm_luminance_range_info *luminance_range =
+		&connector->base.display_info.luminance_range;
+	int ret;
+
+	drm_dbg_kms(&i915->drm, "[CONNECTOR:%d:%s] SDR backlight is controlled through %s\n",
+		    connector->base.base.id, connector->base.name,
+		    dpcd_vs_pwm_str(panel->backlight.edp.intel.sdr_uses_aux));
+
+	if (!panel->backlight.edp.intel.sdr_uses_aux) {
+		ret = panel->backlight.pwm_funcs->setup(connector, pipe);
+		if (ret < 0) {
+			drm_err(&i915->drm,
+				"[CONNECTOR:%d:%s] Failed to setup SDR backlight controls through PWM: %d\n",
+				connector->base.base.id, connector->base.name, ret);
+			return ret;
+		}
+	}
+
+	if (luminance_range->max_luminance) {
+		panel->backlight.max = luminance_range->max_luminance;
+		panel->backlight.min = luminance_range->min_luminance;
+	} else {
+		panel->backlight.max = 512;
+		panel->backlight.min = 0;
+	}
+
+	drm_dbg_kms(&i915->drm, "[CONNECTOR:%d:%s] Using AUX HDR interface for backlight control (range %d..%d)\n",
+		    connector->base.base.id, connector->base.name,
+		    panel->backlight.min, panel->backlight.max);
+
+
+	panel->backlight.level = intel_dp_aux_hdr_get_backlight(connector, pipe);
+	panel->backlight.enabled = panel->backlight.level != 0;
+
+	return 0;
+}
+
+/* VESA backlight callbacks */
+static u32 intel_dp_aux_vesa_get_backlight(struct intel_connector *connector, enum pipe unused)
+{
+	return connector->panel.backlight.level;
+}
+
+static void
+intel_dp_aux_vesa_set_backlight(const struct drm_connector_state *conn_state, u32 level)
+{
+	struct intel_connector *connector = to_intel_connector(conn_state->connector);
+	struct intel_panel *panel = &connector->panel;
+	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
+
+	if (!panel->backlight.edp.vesa.info.aux_set) {
+		const u32 pwm_level = intel_backlight_level_to_pwm(connector, level);
+
+		intel_backlight_set_pwm_level(conn_state, pwm_level);
+	}
+
+	drm_edp_backlight_set_level(&intel_dp->aux, &panel->backlight.edp.vesa.info, level);
+}
+
+static void
+intel_dp_aux_vesa_enable_backlight(const struct intel_crtc_state *crtc_state,
+				   const struct drm_connector_state *conn_state, u32 level)
+{
+	struct intel_connector *connector = to_intel_connector(conn_state->connector);
+	struct intel_panel *panel = &connector->panel;
+	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
+
+	if (!panel->backlight.edp.vesa.info.aux_enable) {
+		u32 pwm_level;
+
+		if (!panel->backlight.edp.vesa.info.aux_set)
+			pwm_level = intel_backlight_level_to_pwm(connector, level);
+		else
+			pwm_level = intel_backlight_invert_pwm_level(connector,
+								     panel->backlight.pwm_level_max);
+
+		panel->backlight.pwm_funcs->enable(crtc_state, conn_state, pwm_level);
+	}
+
+	drm_edp_backlight_enable(&intel_dp->aux, &panel->backlight.edp.vesa.info, level);
+}
+
+static void intel_dp_aux_vesa_disable_backlight(const struct drm_connector_state *old_conn_state,
+						u32 level)
+{
+	struct intel_connector *connector = to_intel_connector(old_conn_state->connector);
+	struct intel_panel *panel = &connector->panel;
+	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
+
+	drm_edp_backlight_disable(&intel_dp->aux, &panel->backlight.edp.vesa.info);
+
+	if (!panel->backlight.edp.vesa.info.aux_enable)
+		panel->backlight.pwm_funcs->disable(old_conn_state,
+						    intel_backlight_invert_pwm_level(connector, 0));
+}
+
+static int intel_dp_aux_vesa_setup_backlight(struct intel_connector *connector, enum pipe pipe)
+{
+	struct intel_dp *intel_dp = intel_attached_dp(connector);
+	struct intel_panel *panel = &connector->panel;
+	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
+	u16 current_level;
+	u8 current_mode;
+	int ret;
+
+	ret = drm_edp_backlight_init(&intel_dp->aux, &panel->backlight.edp.vesa.info,
+				     panel->vbt.backlight.pwm_freq_hz, intel_dp->edp_dpcd,
+				     &current_level, &current_mode);
+	if (ret < 0)
+		return ret;
+
+	drm_dbg_kms(&i915->drm, "[CONNECTOR:%d:%s] AUX VESA backlight enable is controlled through %s\n",
+		    connector->base.base.id, connector->base.name,
+		    dpcd_vs_pwm_str(panel->backlight.edp.vesa.info.aux_enable));
+	drm_dbg_kms(&i915->drm, "[CONNECTOR:%d:%s] AUX VESA backlight level is controlled through %s\n",
+		    connector->base.base.id, connector->base.name,
+		    dpcd_vs_pwm_str(panel->backlight.edp.vesa.info.aux_set));
+
+	if (!panel->backlight.edp.vesa.info.aux_set || !panel->backlight.edp.vesa.info.aux_enable) {
+		ret = panel->backlight.pwm_funcs->setup(connector, pipe);
+		if (ret < 0) {
+			drm_err(&i915->drm,
+				"[CONNECTOR:%d:%s] Failed to setup PWM backlight controls for eDP backlight: %d\n",
+				connector->base.base.id, connector->base.name, ret);
+			return ret;
+		}
+	}
+
+	if (panel->backlight.edp.vesa.info.aux_set) {
+		panel->backlight.max = panel->backlight.edp.vesa.info.max;
+		panel->backlight.min = 0;
+		if (current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
+			panel->backlight.level = current_level;
+			panel->backlight.enabled = panel->backlight.level != 0;
+		} else {
+			panel->backlight.level = panel->backlight.max;
+			panel->backlight.enabled = false;
+		}
+	} else {
+		panel->backlight.max = panel->backlight.pwm_level_max;
+		panel->backlight.min = panel->backlight.pwm_level_min;
+		if (current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_PWM) {
+			panel->backlight.level = panel->backlight.pwm_funcs->get(connector, pipe);
+			panel->backlight.enabled = panel->backlight.pwm_enabled;
+		} else {
+			panel->backlight.level = panel->backlight.max;
+			panel->backlight.enabled = false;
+		}
+	}
+
+	drm_dbg_kms(&i915->drm, "[CONNECTOR:%d:%s] Using AUX VESA interface for backlight control\n",
+		    connector->base.base.id, connector->base.name);
+
+	return 0;
+}
+
+static bool
+intel_dp_aux_supports_vesa_backlight(struct intel_connector *connector)
+{
+	struct intel_dp *intel_dp = intel_attached_dp(connector);
+	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
+
+	if (drm_edp_backlight_supported(intel_dp->edp_dpcd)) {
+		drm_dbg_kms(&i915->drm, "[CONNECTOR:%d:%s] AUX Backlight Control Supported!\n",
+			    connector->base.base.id, connector->base.name);
+		return true;
+	}
+	return false;
+}
+
+static const struct intel_panel_bl_funcs intel_dp_hdr_bl_funcs = {
+	.setup = intel_dp_aux_hdr_setup_backlight,
+	.enable = intel_dp_aux_hdr_enable_backlight,
+	.disable = intel_dp_aux_hdr_disable_backlight,
+	.set = intel_dp_aux_hdr_set_backlight,
+	.get = intel_dp_aux_hdr_get_backlight,
+};
+
+static const struct intel_panel_bl_funcs intel_dp_vesa_bl_funcs = {
+	.setup = intel_dp_aux_vesa_setup_backlight,
+	.enable = intel_dp_aux_vesa_enable_backlight,
+	.disable = intel_dp_aux_vesa_disable_backlight,
+	.set = intel_dp_aux_vesa_set_backlight,
+	.get = intel_dp_aux_vesa_get_backlight,
+};
+
+int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
+{
+	struct drm_device *dev = connector->base.dev;
+	struct intel_panel *panel = &connector->panel;
+	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
+	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
+	bool try_intel_interface = false, try_vesa_interface = false;
+
+	/* Check the VBT and user's module parameters to figure out which
+	 * interfaces to probe
+	 */
+	switch (i915->params.enable_dpcd_backlight) {
+	case INTEL_DP_AUX_BACKLIGHT_OFF:
+		return -ENODEV;
+	case INTEL_DP_AUX_BACKLIGHT_AUTO:
+		switch (panel->vbt.backlight.type) {
+		case INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE:
+			try_vesa_interface = true;
+			break;
+		case INTEL_BACKLIGHT_DISPLAY_DDI:
+			try_intel_interface = true;
+			break;
+		default:
+			return -ENODEV;
+		}
+		break;
+	case INTEL_DP_AUX_BACKLIGHT_ON:
+		if (panel->vbt.backlight.type != INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE)
+			try_intel_interface = true;
+
+		try_vesa_interface = true;
+		break;
+	case INTEL_DP_AUX_BACKLIGHT_FORCE_VESA:
+		try_vesa_interface = true;
+		break;
+	case INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL:
+		try_intel_interface = true;
+		break;
+	}
+
+	/*
+	 * Since Intel has their own backlight control interface, the majority of machines out there
+	 * using DPCD backlight controls with Intel GPUs will be using this interface as opposed to
+	 * the VESA interface. However, other GPUs (such as Nvidia's) will always use the VESA
+	 * interface. This means that there's quite a number of panels out there that will advertise
+	 * support for both interfaces, primarily systems with Intel/Nvidia hybrid GPU setups.
+	 *
+	 * There's a catch to this though: on many panels that advertise support for both
+	 * interfaces, the VESA backlight interface will stop working once we've programmed the
+	 * panel with Intel's OUI - which is also required for us to be able to detect Intel's
+	 * backlight interface at all. This means that the only sensible way for us to detect both
+	 * interfaces is to probe for Intel's first, and VESA's second.
+	 */
+	if (try_intel_interface && intel_dp_aux_supports_hdr_backlight(connector)) {
+		drm_dbg_kms(dev, "[CONNECTOR:%d:%s] Using Intel proprietary eDP backlight controls\n",
+			    connector->base.base.id, connector->base.name);
+		panel->backlight.funcs = &intel_dp_hdr_bl_funcs;
+		return 0;
+	}
+
+	if (try_vesa_interface && intel_dp_aux_supports_vesa_backlight(connector)) {
+		drm_dbg_kms(dev, "[CONNECTOR:%d:%s] Using VESA eDP backlight controls\n",
+			    connector->base.base.id, connector->base.name);
+		panel->backlight.funcs = &intel_dp_vesa_bl_funcs;
+		return 0;
+	}
+
+	return -ENODEV;
+}