// 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 #include #include #include #include #include #include #include #include #include #include #include #include #include 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; bool legacy; 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) { struct pwm_state state; int err; pwm_get_state(pb->pwm, &state); if (pb->enabled) return; err = regulator_enable(pb->power_supply); if (err < 0) dev_err(pb->dev, "failed to enable power supply\n"); state.enabled = true; pwm_apply_state(pb->pwm, &state); if (pb->post_pwm_on_delay) msleep(pb->post_pwm_on_delay); if (pb->enable_gpio) gpiod_set_value_cansleep(pb->enable_gpio, 1); pb->enabled = true; } static void pwm_backlight_power_off(struct pwm_bl_data *pb) { struct pwm_state state; pwm_get_state(pb->pwm, &state); if (!pb->enabled) return; if (pb->enable_gpio) gpiod_set_value_cansleep(pb->enable_gpio, 0); if (pb->pwm_off_delay) msleep(pb->pwm_off_delay); state.enabled = false; state.duty_cycle = 0; pwm_apply_state(pb->pwm, &state); regulator_disable(pb->power_supply); pb->enabled = false; } static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness) { unsigned int lth = pb->lth_brightness; struct pwm_state state; u64 duty_cycle; pwm_get_state(pb->pwm, &state); 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 = bl->props.brightness; struct pwm_state state; if (bl->props.power != FB_BLANK_UNBLANK || bl->props.fb_blank != FB_BLANK_UNBLANK || bl->props.state & BL_CORE_FBBLANK) brightness = 0; 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); pwm_apply_state(pb->pwm, &state); pwm_backlight_power_on(pb); } else pwm_backlight_power_off(pb); 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_SCALE 10000 /* luminance scale */ /* * CIE lightness to PWM conversion. * * The CIE 1931 lightness formula is what actually describes how we perceive * light: * Y = (L* / 902.3) if L* ≤ 0.08856 * Y = ((L* + 16) / 116)^3 if L* > 0.08856 * * 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, unsigned int scale) { u64 retval; lightness *= 100; if (lightness <= (8 * scale)) { retval = DIV_ROUND_CLOSEST_ULL(lightness * 10, 9023); } else { retval = int_pow((lightness + (16 * scale)) / 116, 3); retval = DIV_ROUND_CLOSEST_ULL(retval, (scale * scale)); } 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, PWM_LUMINANCE_SCALE) * 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 = 0; unsigned int levels_count; 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); data->enable_gpio = -EINVAL; /* * 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; data->max_brightness = length / sizeof(u32); /* read brightness levels from DT property */ if (data->max_brightness > 0) { size_t size = sizeof(*data->levels) * data->max_brightness; unsigned int i, j, n = 0; data->levels = devm_kzalloc(dev, size, GFP_KERNEL); if (!data->levels) return -ENOMEM; ret = of_property_read_u32_array(node, "brightness-levels", data->levels, data->max_brightness); 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) { if (data->max_brightness < 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. */ for (i = 0; i < data->max_brightness - 1; i++) { if ((data->levels[i + 1] - data->levels[i]) / num_steps) num_levels += num_steps; else num_levels++; } num_levels++; dev_dbg(dev, "new number of brightness levels: %d\n", num_levels); /* * Create a new table of brightness levels with all the * interpolated steps. */ size = sizeof(*table) * num_levels; table = devm_kzalloc(dev, size, GFP_KERNEL); if (!table) return -ENOMEM; /* Fill the interpolated table. */ levels_count = 0; for (i = 0; i < data->max_brightness - 1; i++) { value = data->levels[i]; n = (data->levels[i + 1] - value) / num_steps; if (n > 0) { for (j = 0; j < num_steps; j++) { table[levels_count] = value; value += n; levels_count++; } } else { table[levels_count] = data->levels[i]; levels_count++; } } table[levels_count] = data->levels[i]; /* * 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; /* * Reassign max_brightness value to the new total number * of brightness levels. */ data->max_brightness = num_levels; } data->max_brightness--; } 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 int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb) { struct device_node *node = pb->dev->of_node; /* 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. */ /* if the enable GPIO is disabled, do not enable the backlight */ if (pb->enable_gpio && gpiod_get_value_cansleep(pb->enable_gpio) == 0) return FB_BLANK_POWERDOWN; /* The regulator is disabled, do not enable the backlight */ if (!regulator_is_enabled(pb->power_supply)) return FB_BLANK_POWERDOWN; /* The PWM is disabled, keep it like this */ if (!pwm_is_enabled(pb->pwm)) return FB_BLANK_POWERDOWN; return FB_BLANK_UNBLANK; } 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 device_node *node = pdev->dev.of_node; 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; } /* * Compatibility fallback for drivers still using the integer GPIO * platform data. Must go away soon. */ if (!pb->enable_gpio && gpio_is_valid(data->enable_gpio)) { ret = devm_gpio_request_one(&pdev->dev, data->enable_gpio, GPIOF_OUT_INIT_HIGH, "enable"); if (ret < 0) { dev_err(&pdev->dev, "failed to request GPIO#%d: %d\n", data->enable_gpio, ret); goto err_alloc; } pb->enable_gpio = gpio_to_desc(data->enable_gpio); } /* * If the GPIO is not known to be already configured as output, that * is, if gpiod_get_direction returns either 1 or -EINVAL, change the * direction to output and set the GPIO as active. * Do not force the GPIO to active when it was already output as it * could cause backlight flickering or we would enable the backlight too * early. Leave the decision of the initial backlight state for later. */ if (pb->enable_gpio && gpiod_get_direction(pb->enable_gpio) != 0) gpiod_direction_output(pb->enable_gpio, 1); pb->power_supply = devm_regulator_get(&pdev->dev, "power"); if (IS_ERR(pb->power_supply)) { ret = PTR_ERR(pb->power_supply); goto err_alloc; } pb->pwm = devm_pwm_get(&pdev->dev, NULL); if (IS_ERR(pb->pwm) && PTR_ERR(pb->pwm) != -EPROBE_DEFER && !node) { dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n"); pb->legacy = true; pb->pwm = pwm_request(data->pwm_id, "pwm-backlight"); } 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; } if (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]; pb->levels = data->levels; } } 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; } } 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 * (state.period / pb->scale); memset(&props, 0, sizeof(struct backlight_properties)); 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); if (pb->legacy) pwm_free(pb->pwm); 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 int pwm_backlight_remove(struct platform_device *pdev) { struct backlight_device *bl = platform_get_drvdata(pdev); struct pwm_bl_data *pb = bl_get_data(bl); backlight_device_unregister(bl); pwm_backlight_power_off(pb); if (pb->exit) pb->exit(&pdev->dev); if (pb->legacy) pwm_free(pb->pwm); return 0; } 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); pwm_backlight_power_off(pb); } #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); if (pb->notify) pb->notify(pb->dev, 0); pwm_backlight_power_off(pb); 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 = 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");