[PATCH 05/11] drm/panthor: Fix theoretical IOMEM access in suspended state

[Boris Brezillon]

In theory, our hardirq handler can be called while the device (and
thus the panthor_irq) is suspended, because the IRQ line is shared.
In practice though, in all the designs we've seen, the line is only
shared within the GPU, and because sub-component suspend state is
consistent (all-suspended or all-resumed), we shouldn't end up with
an interrupt triggered while we're suspended.

Fix the problem anyway, if nothing else, for our sanity.

Fixes: 0b2d86670a84 ("drm/panthor: Rework panthor_irq::suspended into panthor_irq::state")
Reported-by: sashiko-bot@xxxxxxxxxx
Closes: https://sashiko.dev/#/patchset/20260625-panthor-signal-from-irq-v4-0-3d2908912afa@xxxxxxxxxxxxx?part=1
Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/panthor/panthor_device.h | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/gpu/drm/panthor/panthor_device.h
index 35679bfa1f3a..a39386bd6382 100644
--- a/drivers/gpu/drm/panthor/panthor_device.h
+++ b/drivers/gpu/drm/panthor/panthor_device.h
@@ -512,9 +512,6 @@ static irqreturn_t panthor_ ## __name ## _irq_raw_handler(int irq, void *data)
 	struct panthor_irq *pirq = data;							\
 	enum panthor_irq_state old_state;							\
 												\
-	if (!gpu_read(pirq->iomem, INT_STAT))							\
-		return IRQ_NONE;								\
-												\
 	guard(spinlock_irqsave)(&pirq->mask_lock);						\
 	old_state = atomic_cmpxchg(&pirq->state,						\
 				   PANTHOR_IRQ_STATE_ACTIVE,					\
@@ -522,6 +519,13 @@ static irqreturn_t panthor_ ## __name ## _irq_raw_handler(int irq, void *data)
 	if (old_state != PANTHOR_IRQ_STATE_ACTIVE)						\
 		return IRQ_NONE;								\
 												\
+	if (!gpu_read(pirq->iomem, INT_STAT)) {							\
+		atomic_cmpxchg(&pirq->state,							\
+			       PANTHOR_IRQ_STATE_PROCESSING,					\
+			       PANTHOR_IRQ_STATE_ACTIVE);					\
+		return IRQ_NONE;								\
+	}											\
+												\
 	gpu_write(pirq->iomem, INT_MASK, 0);							\
 	return IRQ_WAKE_THREAD;									\
 }												\

-- 
2.54.0