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path: root/drivers/video/backlight/pwm_bl.c
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Diffstat (limited to 'drivers/video/backlight/pwm_bl.c')
-rw-r--r--drivers/video/backlight/pwm_bl.c718
1 files changed, 718 insertions, 0 deletions
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
new file mode 100644
index 0000000000..289bd9ce4d
--- /dev/null
+++ b/drivers/video/backlight/pwm_bl.c
@@ -0,0 +1,718 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Simple PWM based backlight control, board code has to setup
+ * 1) pin configuration so PWM waveforms can output
+ * 2) platform_data being correctly configured
+ */
+
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/platform_device.h>
+#include <linux/fb.h>
+#include <linux/backlight.h>
+#include <linux/err.h>
+#include <linux/pwm.h>
+#include <linux/pwm_backlight.h>
+#include <linux/regulator/consumer.h>
+#include <linux/slab.h>
+
+struct pwm_bl_data {
+ struct pwm_device *pwm;
+ struct device *dev;
+ unsigned int lth_brightness;
+ unsigned int *levels;
+ bool enabled;
+ struct regulator *power_supply;
+ struct gpio_desc *enable_gpio;
+ unsigned int scale;
+ unsigned int post_pwm_on_delay;
+ unsigned int pwm_off_delay;
+ int (*notify)(struct device *,
+ int brightness);
+ void (*notify_after)(struct device *,
+ int brightness);
+ int (*check_fb)(struct device *, struct fb_info *);
+ void (*exit)(struct device *);
+};
+
+static void pwm_backlight_power_on(struct pwm_bl_data *pb)
+{
+ int err;
+
+ if (pb->enabled)
+ return;
+
+ if (pb->power_supply) {
+ err = regulator_enable(pb->power_supply);
+ if (err < 0)
+ dev_err(pb->dev, "failed to enable power supply\n");
+ }
+
+ if (pb->post_pwm_on_delay)
+ msleep(pb->post_pwm_on_delay);
+
+ gpiod_set_value_cansleep(pb->enable_gpio, 1);
+
+ pb->enabled = true;
+}
+
+static void pwm_backlight_power_off(struct pwm_bl_data *pb)
+{
+ if (!pb->enabled)
+ return;
+
+ gpiod_set_value_cansleep(pb->enable_gpio, 0);
+
+ if (pb->pwm_off_delay)
+ msleep(pb->pwm_off_delay);
+
+ if (pb->power_supply)
+ regulator_disable(pb->power_supply);
+ pb->enabled = false;
+}
+
+static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness, struct pwm_state *state)
+{
+ unsigned int lth = pb->lth_brightness;
+ u64 duty_cycle;
+
+ if (pb->levels)
+ duty_cycle = pb->levels[brightness];
+ else
+ duty_cycle = brightness;
+
+ duty_cycle *= state->period - lth;
+ do_div(duty_cycle, pb->scale);
+
+ return duty_cycle + lth;
+}
+
+static int pwm_backlight_update_status(struct backlight_device *bl)
+{
+ struct pwm_bl_data *pb = bl_get_data(bl);
+ int brightness = backlight_get_brightness(bl);
+ struct pwm_state state;
+
+ if (pb->notify)
+ brightness = pb->notify(pb->dev, brightness);
+
+ if (brightness > 0) {
+ pwm_get_state(pb->pwm, &state);
+ state.duty_cycle = compute_duty_cycle(pb, brightness, &state);
+ state.enabled = true;
+ pwm_apply_state(pb->pwm, &state);
+
+ pwm_backlight_power_on(pb);
+ } else {
+ pwm_backlight_power_off(pb);
+
+ pwm_get_state(pb->pwm, &state);
+ state.duty_cycle = 0;
+ /*
+ * We cannot assume a disabled PWM to drive its output to the
+ * inactive state. If we have an enable GPIO and/or a regulator
+ * we assume that this isn't relevant and we can disable the PWM
+ * to save power. If however there is neither an enable GPIO nor
+ * a regulator keep the PWM on be sure to get a constant
+ * inactive output.
+ */
+ state.enabled = !pb->power_supply && !pb->enable_gpio;
+ pwm_apply_state(pb->pwm, &state);
+ }
+
+ if (pb->notify_after)
+ pb->notify_after(pb->dev, brightness);
+
+ return 0;
+}
+
+static int pwm_backlight_check_fb(struct backlight_device *bl,
+ struct fb_info *info)
+{
+ struct pwm_bl_data *pb = bl_get_data(bl);
+
+ return !pb->check_fb || pb->check_fb(pb->dev, info);
+}
+
+static const struct backlight_ops pwm_backlight_ops = {
+ .update_status = pwm_backlight_update_status,
+ .check_fb = pwm_backlight_check_fb,
+};
+
+#ifdef CONFIG_OF
+#define PWM_LUMINANCE_SHIFT 16
+#define PWM_LUMINANCE_SCALE (1 << PWM_LUMINANCE_SHIFT) /* luminance scale */
+
+/*
+ * CIE lightness to PWM conversion.
+ *
+ * The CIE 1931 lightness formula is what actually describes how we perceive
+ * light:
+ * Y = (L* / 903.3) if L* ≤ 8
+ * Y = ((L* + 16) / 116)^3 if L* > 8
+ *
+ * Where Y is the luminance, the amount of light coming out of the screen, and
+ * is a number between 0.0 and 1.0; and L* is the lightness, how bright a human
+ * perceives the screen to be, and is a number between 0 and 100.
+ *
+ * The following function does the fixed point maths needed to implement the
+ * above formula.
+ */
+static u64 cie1931(unsigned int lightness)
+{
+ u64 retval;
+
+ /*
+ * @lightness is given as a number between 0 and 1, expressed
+ * as a fixed-point number in scale
+ * PWM_LUMINANCE_SCALE. Convert to a percentage, still
+ * expressed as a fixed-point number, so the above formulas
+ * can be applied.
+ */
+ lightness *= 100;
+ if (lightness <= (8 * PWM_LUMINANCE_SCALE)) {
+ retval = DIV_ROUND_CLOSEST(lightness * 10, 9033);
+ } else {
+ retval = (lightness + (16 * PWM_LUMINANCE_SCALE)) / 116;
+ retval *= retval * retval;
+ retval += 1ULL << (2*PWM_LUMINANCE_SHIFT - 1);
+ retval >>= 2*PWM_LUMINANCE_SHIFT;
+ }
+
+ return retval;
+}
+
+/*
+ * Create a default correction table for PWM values to create linear brightness
+ * for LED based backlights using the CIE1931 algorithm.
+ */
+static
+int pwm_backlight_brightness_default(struct device *dev,
+ struct platform_pwm_backlight_data *data,
+ unsigned int period)
+{
+ unsigned int i;
+ u64 retval;
+
+ /*
+ * Once we have 4096 levels there's little point going much higher...
+ * neither interactive sliders nor animation benefits from having
+ * more values in the table.
+ */
+ data->max_brightness =
+ min((int)DIV_ROUND_UP(period, fls(period)), 4096);
+
+ data->levels = devm_kcalloc(dev, data->max_brightness,
+ sizeof(*data->levels), GFP_KERNEL);
+ if (!data->levels)
+ return -ENOMEM;
+
+ /* Fill the table using the cie1931 algorithm */
+ for (i = 0; i < data->max_brightness; i++) {
+ retval = cie1931((i * PWM_LUMINANCE_SCALE) /
+ data->max_brightness) * period;
+ retval = DIV_ROUND_CLOSEST_ULL(retval, PWM_LUMINANCE_SCALE);
+ if (retval > UINT_MAX)
+ return -EINVAL;
+ data->levels[i] = (unsigned int)retval;
+ }
+
+ data->dft_brightness = data->max_brightness / 2;
+ data->max_brightness--;
+
+ return 0;
+}
+
+static int pwm_backlight_parse_dt(struct device *dev,
+ struct platform_pwm_backlight_data *data)
+{
+ struct device_node *node = dev->of_node;
+ unsigned int num_levels;
+ unsigned int num_steps = 0;
+ struct property *prop;
+ unsigned int *table;
+ int length;
+ u32 value;
+ int ret;
+
+ if (!node)
+ return -ENODEV;
+
+ memset(data, 0, sizeof(*data));
+
+ /*
+ * These values are optional and set as 0 by default, the out values
+ * are modified only if a valid u32 value can be decoded.
+ */
+ of_property_read_u32(node, "post-pwm-on-delay-ms",
+ &data->post_pwm_on_delay);
+ of_property_read_u32(node, "pwm-off-delay-ms", &data->pwm_off_delay);
+
+ /*
+ * Determine the number of brightness levels, if this property is not
+ * set a default table of brightness levels will be used.
+ */
+ prop = of_find_property(node, "brightness-levels", &length);
+ if (!prop)
+ return 0;
+
+ num_levels = length / sizeof(u32);
+
+ /* read brightness levels from DT property */
+ if (num_levels > 0) {
+ data->levels = devm_kcalloc(dev, num_levels,
+ sizeof(*data->levels), GFP_KERNEL);
+ if (!data->levels)
+ return -ENOMEM;
+
+ ret = of_property_read_u32_array(node, "brightness-levels",
+ data->levels,
+ num_levels);
+ if (ret < 0)
+ return ret;
+
+ ret = of_property_read_u32(node, "default-brightness-level",
+ &value);
+ if (ret < 0)
+ return ret;
+
+ data->dft_brightness = value;
+
+ /*
+ * This property is optional, if is set enables linear
+ * interpolation between each of the values of brightness levels
+ * and creates a new pre-computed table.
+ */
+ of_property_read_u32(node, "num-interpolated-steps",
+ &num_steps);
+
+ /*
+ * Make sure that there is at least two entries in the
+ * brightness-levels table, otherwise we can't interpolate
+ * between two points.
+ */
+ if (num_steps) {
+ unsigned int num_input_levels = num_levels;
+ unsigned int i;
+ u32 x1, x2, x, dx;
+ u32 y1, y2;
+ s64 dy;
+
+ if (num_input_levels < 2) {
+ dev_err(dev, "can't interpolate\n");
+ return -EINVAL;
+ }
+
+ /*
+ * Recalculate the number of brightness levels, now
+ * taking in consideration the number of interpolated
+ * steps between two levels.
+ */
+ num_levels = (num_input_levels - 1) * num_steps + 1;
+ dev_dbg(dev, "new number of brightness levels: %d\n",
+ num_levels);
+
+ /*
+ * Create a new table of brightness levels with all the
+ * interpolated steps.
+ */
+ table = devm_kcalloc(dev, num_levels, sizeof(*table),
+ GFP_KERNEL);
+ if (!table)
+ return -ENOMEM;
+ /*
+ * Fill the interpolated table[x] = y
+ * by draw lines between each (x1, y1) to (x2, y2).
+ */
+ dx = num_steps;
+ for (i = 0; i < num_input_levels - 1; i++) {
+ x1 = i * dx;
+ x2 = x1 + dx;
+ y1 = data->levels[i];
+ y2 = data->levels[i + 1];
+ dy = (s64)y2 - y1;
+
+ for (x = x1; x < x2; x++) {
+ table[x] = y1 +
+ div_s64(dy * (x - x1), dx);
+ }
+ }
+ /* Fill in the last point, since no line starts here. */
+ table[x2] = y2;
+
+ /*
+ * As we use interpolation lets remove current
+ * brightness levels table and replace for the
+ * new interpolated table.
+ */
+ devm_kfree(dev, data->levels);
+ data->levels = table;
+ }
+
+ data->max_brightness = num_levels - 1;
+ }
+
+ return 0;
+}
+
+static const struct of_device_id pwm_backlight_of_match[] = {
+ { .compatible = "pwm-backlight" },
+ { }
+};
+
+MODULE_DEVICE_TABLE(of, pwm_backlight_of_match);
+#else
+static int pwm_backlight_parse_dt(struct device *dev,
+ struct platform_pwm_backlight_data *data)
+{
+ return -ENODEV;
+}
+
+static
+int pwm_backlight_brightness_default(struct device *dev,
+ struct platform_pwm_backlight_data *data,
+ unsigned int period)
+{
+ return -ENODEV;
+}
+#endif
+
+static bool pwm_backlight_is_linear(struct platform_pwm_backlight_data *data)
+{
+ unsigned int nlevels = data->max_brightness + 1;
+ unsigned int min_val = data->levels[0];
+ unsigned int max_val = data->levels[nlevels - 1];
+ /*
+ * Multiplying by 128 means that even in pathological cases such
+ * as (max_val - min_val) == nlevels the error at max_val is less
+ * than 1%.
+ */
+ unsigned int slope = (128 * (max_val - min_val)) / nlevels;
+ unsigned int margin = (max_val - min_val) / 20; /* 5% */
+ int i;
+
+ for (i = 1; i < nlevels; i++) {
+ unsigned int linear_value = min_val + ((i * slope) / 128);
+ unsigned int delta = abs(linear_value - data->levels[i]);
+
+ if (delta > margin)
+ return false;
+ }
+
+ return true;
+}
+
+static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb)
+{
+ struct device_node *node = pb->dev->of_node;
+ bool active = true;
+
+ /*
+ * If the enable GPIO is present, observable (either as input
+ * or output) and off then the backlight is not currently active.
+ * */
+ if (pb->enable_gpio && gpiod_get_value_cansleep(pb->enable_gpio) == 0)
+ active = false;
+
+ if (pb->power_supply && !regulator_is_enabled(pb->power_supply))
+ active = false;
+
+ if (!pwm_is_enabled(pb->pwm))
+ active = false;
+
+ /*
+ * Synchronize the enable_gpio with the observed state of the
+ * hardware.
+ */
+ gpiod_direction_output(pb->enable_gpio, active);
+
+ /*
+ * Do not change pb->enabled here! pb->enabled essentially
+ * tells us if we own one of the regulator's use counts and
+ * right now we do not.
+ */
+
+ /* Not booted with device tree or no phandle link to the node */
+ if (!node || !node->phandle)
+ return FB_BLANK_UNBLANK;
+
+ /*
+ * If the driver is probed from the device tree and there is a
+ * phandle link pointing to the backlight node, it is safe to
+ * assume that another driver will enable the backlight at the
+ * appropriate time. Therefore, if it is disabled, keep it so.
+ */
+ return active ? FB_BLANK_UNBLANK: FB_BLANK_POWERDOWN;
+}
+
+static int pwm_backlight_probe(struct platform_device *pdev)
+{
+ struct platform_pwm_backlight_data *data = dev_get_platdata(&pdev->dev);
+ struct platform_pwm_backlight_data defdata;
+ struct backlight_properties props;
+ struct backlight_device *bl;
+ struct pwm_bl_data *pb;
+ struct pwm_state state;
+ unsigned int i;
+ int ret;
+
+ if (!data) {
+ ret = pwm_backlight_parse_dt(&pdev->dev, &defdata);
+ if (ret < 0) {
+ dev_err(&pdev->dev, "failed to find platform data\n");
+ return ret;
+ }
+
+ data = &defdata;
+ }
+
+ if (data->init) {
+ ret = data->init(&pdev->dev);
+ if (ret < 0)
+ return ret;
+ }
+
+ pb = devm_kzalloc(&pdev->dev, sizeof(*pb), GFP_KERNEL);
+ if (!pb) {
+ ret = -ENOMEM;
+ goto err_alloc;
+ }
+
+ pb->notify = data->notify;
+ pb->notify_after = data->notify_after;
+ pb->check_fb = data->check_fb;
+ pb->exit = data->exit;
+ pb->dev = &pdev->dev;
+ pb->enabled = false;
+ pb->post_pwm_on_delay = data->post_pwm_on_delay;
+ pb->pwm_off_delay = data->pwm_off_delay;
+
+ pb->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable",
+ GPIOD_ASIS);
+ if (IS_ERR(pb->enable_gpio)) {
+ ret = PTR_ERR(pb->enable_gpio);
+ goto err_alloc;
+ }
+
+ pb->power_supply = devm_regulator_get_optional(&pdev->dev, "power");
+ if (IS_ERR(pb->power_supply)) {
+ ret = PTR_ERR(pb->power_supply);
+ if (ret == -ENODEV)
+ pb->power_supply = NULL;
+ else
+ goto err_alloc;
+ }
+
+ pb->pwm = devm_pwm_get(&pdev->dev, NULL);
+ if (IS_ERR(pb->pwm)) {
+ ret = PTR_ERR(pb->pwm);
+ if (ret != -EPROBE_DEFER)
+ dev_err(&pdev->dev, "unable to request PWM\n");
+ goto err_alloc;
+ }
+
+ dev_dbg(&pdev->dev, "got pwm for backlight\n");
+
+ /* Sync up PWM state. */
+ pwm_init_state(pb->pwm, &state);
+
+ /*
+ * The DT case will set the pwm_period_ns field to 0 and store the
+ * period, parsed from the DT, in the PWM device. For the non-DT case,
+ * set the period from platform data if it has not already been set
+ * via the PWM lookup table.
+ */
+ if (!state.period && (data->pwm_period_ns > 0))
+ state.period = data->pwm_period_ns;
+
+ ret = pwm_apply_state(pb->pwm, &state);
+ if (ret) {
+ dev_err(&pdev->dev, "failed to apply initial PWM state: %d\n",
+ ret);
+ goto err_alloc;
+ }
+
+ memset(&props, 0, sizeof(struct backlight_properties));
+
+ if (data->levels) {
+ pb->levels = data->levels;
+
+ /*
+ * For the DT case, only when brightness levels is defined
+ * data->levels is filled. For the non-DT case, data->levels
+ * can come from platform data, however is not usual.
+ */
+ for (i = 0; i <= data->max_brightness; i++)
+ if (data->levels[i] > pb->scale)
+ pb->scale = data->levels[i];
+
+ if (pwm_backlight_is_linear(data))
+ props.scale = BACKLIGHT_SCALE_LINEAR;
+ else
+ props.scale = BACKLIGHT_SCALE_NON_LINEAR;
+ } else if (!data->max_brightness) {
+ /*
+ * If no brightness levels are provided and max_brightness is
+ * not set, use the default brightness table. For the DT case,
+ * max_brightness is set to 0 when brightness levels is not
+ * specified. For the non-DT case, max_brightness is usually
+ * set to some value.
+ */
+
+ /* Get the PWM period (in nanoseconds) */
+ pwm_get_state(pb->pwm, &state);
+
+ ret = pwm_backlight_brightness_default(&pdev->dev, data,
+ state.period);
+ if (ret < 0) {
+ dev_err(&pdev->dev,
+ "failed to setup default brightness table\n");
+ goto err_alloc;
+ }
+
+ for (i = 0; i <= data->max_brightness; i++) {
+ if (data->levels[i] > pb->scale)
+ pb->scale = data->levels[i];
+
+ pb->levels = data->levels;
+ }
+
+ props.scale = BACKLIGHT_SCALE_NON_LINEAR;
+ } else {
+ /*
+ * That only happens for the non-DT case, where platform data
+ * sets the max_brightness value.
+ */
+ pb->scale = data->max_brightness;
+ }
+
+ pb->lth_brightness = data->lth_brightness * (div_u64(state.period,
+ pb->scale));
+
+ props.type = BACKLIGHT_RAW;
+ props.max_brightness = data->max_brightness;
+ bl = backlight_device_register(dev_name(&pdev->dev), &pdev->dev, pb,
+ &pwm_backlight_ops, &props);
+ if (IS_ERR(bl)) {
+ dev_err(&pdev->dev, "failed to register backlight\n");
+ ret = PTR_ERR(bl);
+ goto err_alloc;
+ }
+
+ if (data->dft_brightness > data->max_brightness) {
+ dev_warn(&pdev->dev,
+ "invalid default brightness level: %u, using %u\n",
+ data->dft_brightness, data->max_brightness);
+ data->dft_brightness = data->max_brightness;
+ }
+
+ bl->props.brightness = data->dft_brightness;
+ bl->props.power = pwm_backlight_initial_power_state(pb);
+ backlight_update_status(bl);
+
+ platform_set_drvdata(pdev, bl);
+ return 0;
+
+err_alloc:
+ if (data->exit)
+ data->exit(&pdev->dev);
+ return ret;
+}
+
+static void pwm_backlight_remove(struct platform_device *pdev)
+{
+ struct backlight_device *bl = platform_get_drvdata(pdev);
+ struct pwm_bl_data *pb = bl_get_data(bl);
+ struct pwm_state state;
+
+ backlight_device_unregister(bl);
+ pwm_backlight_power_off(pb);
+ pwm_get_state(pb->pwm, &state);
+ state.duty_cycle = 0;
+ state.enabled = false;
+ pwm_apply_state(pb->pwm, &state);
+
+ if (pb->exit)
+ pb->exit(&pdev->dev);
+}
+
+static void pwm_backlight_shutdown(struct platform_device *pdev)
+{
+ struct backlight_device *bl = platform_get_drvdata(pdev);
+ struct pwm_bl_data *pb = bl_get_data(bl);
+ struct pwm_state state;
+
+ pwm_backlight_power_off(pb);
+ pwm_get_state(pb->pwm, &state);
+ state.duty_cycle = 0;
+ state.enabled = false;
+ pwm_apply_state(pb->pwm, &state);
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int pwm_backlight_suspend(struct device *dev)
+{
+ struct backlight_device *bl = dev_get_drvdata(dev);
+ struct pwm_bl_data *pb = bl_get_data(bl);
+ struct pwm_state state;
+
+ if (pb->notify)
+ pb->notify(pb->dev, 0);
+
+ pwm_backlight_power_off(pb);
+
+ /*
+ * Note that disabling the PWM doesn't guarantee that the output stays
+ * at its inactive state. However without the PWM disabled, the PWM
+ * driver refuses to suspend. So disable here even though this might
+ * enable the backlight on poorly designed boards.
+ */
+ pwm_get_state(pb->pwm, &state);
+ state.duty_cycle = 0;
+ state.enabled = false;
+ pwm_apply_state(pb->pwm, &state);
+
+ if (pb->notify_after)
+ pb->notify_after(pb->dev, 0);
+
+ return 0;
+}
+
+static int pwm_backlight_resume(struct device *dev)
+{
+ struct backlight_device *bl = dev_get_drvdata(dev);
+
+ backlight_update_status(bl);
+
+ return 0;
+}
+#endif
+
+static const struct dev_pm_ops pwm_backlight_pm_ops = {
+#ifdef CONFIG_PM_SLEEP
+ .suspend = pwm_backlight_suspend,
+ .resume = pwm_backlight_resume,
+ .poweroff = pwm_backlight_suspend,
+ .restore = pwm_backlight_resume,
+#endif
+};
+
+static struct platform_driver pwm_backlight_driver = {
+ .driver = {
+ .name = "pwm-backlight",
+ .pm = &pwm_backlight_pm_ops,
+ .of_match_table = of_match_ptr(pwm_backlight_of_match),
+ },
+ .probe = pwm_backlight_probe,
+ .remove_new = pwm_backlight_remove,
+ .shutdown = pwm_backlight_shutdown,
+};
+
+module_platform_driver(pwm_backlight_driver);
+
+MODULE_DESCRIPTION("PWM based Backlight Driver");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:pwm-backlight");