From daa37361518bf2d1f591bbdaa7c68b2a43d7af48 Mon Sep 17 00:00:00 2001 From: Linus Walleij Date: Thu, 15 Jul 2021 13:36:36 +0200 Subject: [PATCH 1/2] backlight: ktd253: Stabilize backlight Remove interrupt disablement during backlight setting. It is way to dangerous and makes platforms instable by having it miss vblank IRQs leading to the graphics derailing. The code is using ndelay() which is not available on platforms such as ARM and will result in 32 * udelay(1) which is substantial. Add some code to detect if an interrupt occurs during the tight loop and in that case just redo it from the top. Fixes: 5317f37e48b9 ("backlight: Add Kinetic KTD253 backlight driver") Cc: Stephan Gerhold Reported-by: newbyte@disroot.org Reviewed-by: Daniel Thompson Signed-off-by: Linus Walleij Signed-off-by: Lee Jones --- drivers/video/backlight/ktd253-backlight.c | 75 ++++++++++++++++------ 1 file changed, 55 insertions(+), 20 deletions(-) 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); From 79fad92f2e596f5a8dd085788a24f540263ef887 Mon Sep 17 00:00:00 2001 From: Daniel Thompson Date: Thu, 22 Jul 2021 15:46:23 +0100 Subject: [PATCH 2/2] backlight: pwm_bl: Improve bootloader/kernel device handover Currently there are (at least) two problems in the way pwm_bl starts managing the enable_gpio pin. Both occur when the backlight is initially off and the driver finds the pin not already in output mode and, as a result, unconditionally switches it to output-mode and asserts the signal. Problem 1: This could cause the backlight to flicker since, at this stage in driver initialisation, we have no idea what the PWM and regulator are doing (an unconfigured PWM could easily "rest" at 100% duty cycle). Problem 2: This will cause us not to correctly honour the post_pwm_on_delay (which also risks flickers). Fix this by moving the code to configure the GPIO output mode until after we have examines the handover state. That allows us to initialize enable_gpio to off if the backlight is currently off and on if the backlight is on. Cc: stable@vger.kernel.org Reported-by: Marek Vasut Signed-off-by: Daniel Thompson Acked-by: Marek Vasut Tested-by: Marek Vasut Signed-off-by: Lee Jones --- drivers/video/backlight/pwm_bl.c | 54 +++++++++++++++++--------------- 1 file changed, 28 insertions(+), 26 deletions(-) diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index e48fded3e414..8d8959a70e44 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -409,6 +409,33 @@ static bool pwm_backlight_is_linear(struct platform_pwm_backlight_data *data) 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 (!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. + */ + if (pb->enable_gpio) + 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) @@ -420,20 +447,7 @@ static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb) * 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; + return active ? FB_BLANK_UNBLANK: FB_BLANK_POWERDOWN; } static int pwm_backlight_probe(struct platform_device *pdev) @@ -486,18 +500,6 @@ static int pwm_backlight_probe(struct platform_device *pdev) goto err_alloc; } - /* - * 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);