[PATCH v2 03/10] drm/bridge: analogix_dp: Add IRQF_ONESHOT and simplify IRQ handling

[Damon Ding]

The threaded IRQ is requested without IRQF_ONESHOT, allowing hardirq to
preempt the threaded handler. This creates a read-modify-write race on
HPD interrupt mask registers between the hardirq mute and thread unmute
operations.

Add IRQF_ONESHOT to keep the IRQ line masked during thread execution,
which eliminates the race and makes the per-event mute/unmute calls in
hardirq and thread handlers redundant. Move interrupt status clearing
to the beginning of the threaded handler, before
drm_helper_hpd_irq_event(), to avoid losing events that arrive during
the event handling.

Signed-off-by: Damon Ding <damon.ding at rock-chips.com>
---
 .../gpu/drm/bridge/analogix/analogix_dp_core.c  | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
index 7ef8ef812b55..4fe248e66515 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
@@ -707,10 +707,8 @@ static irqreturn_t analogix_dp_hardirq(int irq, void *arg)
 	u32 irq_type;
 
 	irq_type = analogix_dp_get_irq_type(dp);
-	if (irq_type) {
-		analogix_dp_mute_hpd_interrupt(dp);
+	if (irq_type)
 		ret = IRQ_WAKE_THREAD;
-	}
 
 	return ret;
 }
@@ -721,6 +719,9 @@ static irqreturn_t analogix_dp_irq_thread(int irq, void *arg)
 	u32 irq_type;
 
 	irq_type = analogix_dp_get_irq_type(dp);
+	if (irq_type)
+		analogix_dp_clear_hotplug_interrupts(dp);
+
 	if (irq_type & DP_IRQ_TYPE_HP_CABLE_IN ||
 	    irq_type & DP_IRQ_TYPE_HP_CABLE_OUT) {
 		dev_dbg(dp->dev, "Detected cable status changed!\n");
@@ -728,11 +729,6 @@ static irqreturn_t analogix_dp_irq_thread(int irq, void *arg)
 			drm_helper_hpd_irq_event(dp->drm_dev);
 	}
 
-	if (irq_type) {
-		analogix_dp_clear_hotplug_interrupts(dp);
-		analogix_dp_unmute_hpd_interrupt(dp);
-	}
-
 	return IRQ_HANDLED;
 }
 
@@ -1403,10 +1399,11 @@ analogix_dp_probe(struct device *dev, struct analogix_dp_plat_data *plat_data)
 		 * that we can get the current state of the GPIO.
 		 */
 		dp->irq = gpiod_to_irq(dp->hpd_gpiod);
-		irq_flags = IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING | IRQF_NO_AUTOEN;
+		irq_flags = IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING | IRQF_NO_AUTOEN |
+			    IRQF_ONESHOT;
 	} else {
 		dp->irq = platform_get_irq(pdev, 0);
-		irq_flags = IRQF_NO_AUTOEN;
+		irq_flags = IRQF_NO_AUTOEN | IRQF_ONESHOT;
 	}
 
 	if (dp->irq == -ENXIO) {
-- 
2.34.1