diff --git a/drivers/video/backlight/ktd253-backlight.c b/drivers/video/backlight/ktd253-backlight.c index a7df5bcca9da..37aa5a669530 100644 --- a/drivers/video/backlight/ktd253-backlight.c +++ b/drivers/video/backlight/ktd253-backlight.c @@ -25,6 +25,7 @@ #define KTD253_T_LOW_NS (200 + 10) /* Additional 10ns as safety factor */ #define KTD253_T_HIGH_NS (200 + 10) /* Additional 10ns as safety factor */ +#define KTD253_T_OFF_CRIT_NS 100000 /* 100 us, now it doesn't look good */ #define KTD253_T_OFF_MS 3 struct ktd253_backlight { @@ -34,13 +35,50 @@ struct ktd253_backlight { u16 ratio; }; +static void ktd253_backlight_set_max_ratio(struct ktd253_backlight *ktd253) +{ + gpiod_set_value_cansleep(ktd253->gpiod, 1); + ndelay(KTD253_T_HIGH_NS); + /* We always fall back to this when we power on */ +} + +static int ktd253_backlight_stepdown(struct ktd253_backlight *ktd253) +{ + /* + * These GPIO operations absolutely can NOT sleep so no _cansleep + * suffixes, and no using GPIO expanders on slow buses for this! + * + * The maximum number of cycles of the loop is 32 so the time taken + * should nominally be: + * (T_LOW_NS + T_HIGH_NS + loop_time) * 32 + * + * Architectures do not always support ndelay() and we will get a few us + * instead. If we get to a critical time limit an interrupt has likely + * occured in the low part of the loop and we need to restart from the + * top so we have the backlight in a known state. + */ + u64 ns; + + ns = ktime_get_ns(); + gpiod_set_value(ktd253->gpiod, 0); + ndelay(KTD253_T_LOW_NS); + gpiod_set_value(ktd253->gpiod, 1); + ns = ktime_get_ns() - ns; + if (ns >= KTD253_T_OFF_CRIT_NS) { + dev_err(ktd253->dev, "PCM on backlight took too long (%llu ns)\n", ns); + return -EAGAIN; + } + ndelay(KTD253_T_HIGH_NS); + return 0; +} + static int ktd253_backlight_update_status(struct backlight_device *bl) { struct ktd253_backlight *ktd253 = bl_get_data(bl); int brightness = backlight_get_brightness(bl); u16 target_ratio; u16 current_ratio = ktd253->ratio; - unsigned long flags; + int ret; dev_dbg(ktd253->dev, "new brightness/ratio: %d/32\n", brightness); @@ -62,37 +100,34 @@ static int ktd253_backlight_update_status(struct backlight_device *bl) } if (current_ratio == 0) { - gpiod_set_value_cansleep(ktd253->gpiod, 1); - ndelay(KTD253_T_HIGH_NS); - /* We always fall back to this when we power on */ + ktd253_backlight_set_max_ratio(ktd253); current_ratio = KTD253_MAX_RATIO; } - /* - * WARNING: - * The loop to set the correct current level is performed - * with interrupts disabled as it is timing critical. - * The maximum number of cycles of the loop is 32 - * so the time taken will be (T_LOW_NS + T_HIGH_NS + loop_time) * 32, - */ - local_irq_save(flags); while (current_ratio != target_ratio) { /* * These GPIO operations absolutely can NOT sleep so no * _cansleep suffixes, and no using GPIO expanders on * slow buses for this! */ - gpiod_set_value(ktd253->gpiod, 0); - ndelay(KTD253_T_LOW_NS); - gpiod_set_value(ktd253->gpiod, 1); - ndelay(KTD253_T_HIGH_NS); - /* After 1/32 we loop back to 32/32 */ - if (current_ratio == KTD253_MIN_RATIO) + ret = ktd253_backlight_stepdown(ktd253); + if (ret == -EAGAIN) { + /* + * Something disturbed the backlight setting code when + * running so we need to bring the PWM back to a known + * state. This shouldn't happen too much. + */ + gpiod_set_value_cansleep(ktd253->gpiod, 0); + msleep(KTD253_T_OFF_MS); + ktd253_backlight_set_max_ratio(ktd253); current_ratio = KTD253_MAX_RATIO; - else + } else if (current_ratio == KTD253_MIN_RATIO) { + /* After 1/32 we loop back to 32/32 */ + current_ratio = KTD253_MAX_RATIO; + } else { current_ratio--; + } } - local_irq_restore(flags); ktd253->ratio = current_ratio; dev_dbg(ktd253->dev, "new ratio set to %d/32\n", target_ratio);