diff options
Diffstat (limited to 'drivers/video/backlight/pwm_bl.c')
| -rw-r--r-- | drivers/video/backlight/pwm_bl.c | 30 |
1 files changed, 8 insertions, 22 deletions
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index 20d379ac8440..2201b8c78641 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -1,8 +1,6 @@ // SPDX-License-Identifier: GPL-2.0-only /* - * linux/drivers/video/backlight/pwm_bl.c - * - * simple PWM based backlight control, board code has to setup + * Simple PWM based backlight control, board code has to setup * 1) pin configuration so PWM waveforms can output * 2) platform_data being correctly configured */ @@ -191,29 +189,17 @@ int pwm_backlight_brightness_default(struct device *dev, struct platform_pwm_backlight_data *data, unsigned int period) { - unsigned int counter = 0; - unsigned int i, n; + unsigned int i; u64 retval; /* - * Count the number of bits needed to represent the period number. The - * number of bits is used to calculate the number of levels used for the - * brightness-levels table, the purpose of this calculation is have a - * pre-computed table with enough levels to get linear brightness - * perception. The period is divided by the number of bits so for a - * 8-bit PWM we have 255 / 8 = 32 brightness levels or for a 16-bit PWM - * we have 65535 / 16 = 4096 brightness levels. - * - * Note that this method is based on empirical testing on different - * devices with PWM of 8 and 16 bits of resolution. + * 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. */ - n = period; - while (n) { - counter += n % 2; - n >>= 1; - } + data->max_brightness = + min((int)DIV_ROUND_UP(period, fls(period)), 4096); - data->max_brightness = DIV_ROUND_UP(period, counter); data->levels = devm_kcalloc(dev, data->max_brightness, sizeof(*data->levels), GFP_KERNEL); if (!data->levels) @@ -705,5 +691,5 @@ static struct platform_driver pwm_backlight_driver = { module_platform_driver(pwm_backlight_driver); MODULE_DESCRIPTION("PWM based Backlight Driver"); -MODULE_LICENSE("GPL"); +MODULE_LICENSE("GPL v2"); MODULE_ALIAS("platform:pwm-backlight"); |