diff options
Diffstat (limited to 'drivers/video/backlight/pwm_bl.c')
| -rw-r--r-- | drivers/video/backlight/pwm_bl.c | 718 |
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"); |