@@ -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);