Merge tag 'backlight-next-5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight

Pull backlight updates from Lee Jones:
 "Fix-ups:
   - Improve bootloader/kernel device handover

  Bug Fixes:
   - Stabilise backlight in ktd253 driver"

* tag 'backlight-next-5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight:
  backlight: pwm_bl: Improve bootloader/kernel device handover
  backlight: ktd253: Stabilize backlight

2 files changed, 83 insertions, 46 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 if (current_ratio == KTD253_MIN_RATIO) {
+			/* After 1/32 we loop back to 32/32 */
 			current_ratio = KTD253_MAX_RATIO;
-		else
+		} else {
 			current_ratio--;
+		}
 	}
-	local_irq_restore(flags);
 	ktd253->ratio = current_ratio;
 
 	dev_dbg(ktd253->dev, "new ratio set to %d/32\n", target_ratio);
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);