[PATCH v2 4/9] media: chips-media: wave5: ack the interrupt after dispatching it

["Jackson.lee" <jackson.lee@chipsnmedia.com>]

From: Jackson Lee <jackson.lee@chipsnmedia.com>

W5_RET_QUEUE_CMD_DONE_INST is written by both the driver and the VPU:
the VPU sets the bit of every instance whose command completed, and the
driver clears the bits it has consumed. The driver does that as a
read-modify-write over a snapshot taken at the top of the handler, so
any bit the VPU adds in between is erased.

The firmware does not update that register, for any reason, until the
host acknowledges the interrupt through W5_VPU_VINT_REASON_CLR and
W5_VPU_VINT_CLEAR, so leaving the interrupt unacknowledged for the whole
dispatch is what keeps the register still. Acknowledging first opened
the race instead: the firmware could rewrite the register, and the
write-back then dropped the instance it had just added. That instance is
never reported again -- its queue count stays non-zero and no further
completion arrives, so it stops decoding for good while the others keep
running.

Move both acknowledge writes past the dispatch loop. The re-read of
W5_VPU_VINT_REASON that tried to narrow the window is no longer needed.

Fixes: 9707a6254a8a ("media: chips-media: wave5: Add the v4l2 layer")
Cc: stable@vger.kernel.org
Tested-by: Brandon Brnich <b-brnich@ti.com>
Signed-off-by: Jackson Lee <jackson.lee@chipsnmedia.com>
Signed-off-by: Nas Chung <nas.chung@chipsnmedia.com>
---
 .../platform/chips-media/wave5/wave5-vpu.c    | 29 ++++++++++++-------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/drivers/media/platform/chips-media/wave5/wave5-vpu.c b/drivers/media/platform/chips-media/wave5/wave5-vpu.c
index 76d57c6b636a..6a5b646ff0f9 100644
--- a/drivers/media/platform/chips-media/wave5/wave5-vpu.c
+++ b/drivers/media/platform/chips-media/wave5/wave5-vpu.c
@@ -51,7 +51,6 @@ static void wave5_vpu_handle_irq(void *dev_id)
 	u32 seq_done;
 	u32 cmd_done;
 	u32 irq_reason;
-	u32 irq_subreason;
 	struct vpu_instance *inst, *tmp;
 	struct vpu_device *dev = dev_id;
 	int val;
@@ -60,8 +59,6 @@ static void wave5_vpu_handle_irq(void *dev_id)
 	irq_reason = wave5_vdi_read_register(dev, W5_VPU_VINT_REASON);
 	seq_done = wave5_vdi_read_register(dev, W5_RET_SEQ_DONE_INSTANCE_INFO);
 	cmd_done = wave5_vdi_read_register(dev, W5_RET_QUEUE_CMD_DONE_INST);
-	wave5_vdi_write_register(dev, W5_VPU_VINT_REASON_CLR, irq_reason);
-	wave5_vdi_write_register(dev, W5_VPU_VINT_CLEAR, 0x1);
 
 	spin_lock_irqsave(&dev->irq_spinlock, flags);
 	list_for_each_entry_safe(inst, tmp, &dev->instances, list) {
@@ -86,14 +83,10 @@ static void wave5_vpu_handle_irq(void *dev_id)
 		    irq_reason & BIT(INT_WAVE5_ENC_PIC)) {
 			if (cmd_done & BIT(inst->id)) {
 				cmd_done &= ~BIT(inst->id);
-				if (dev->irq >= 0) {
-					irq_subreason =
-						wave5_vdi_read_register(dev, W5_VPU_VINT_REASON);
-					if (!(irq_subreason & BIT(INT_WAVE5_DEC_PIC)))
-						wave5_vdi_write_register(dev,
-									 W5_RET_QUEUE_CMD_DONE_INST,
-									 cmd_done);
-				}
+				if (dev->irq >= 0)
+					wave5_vdi_write_register(dev,
+								 W5_RET_QUEUE_CMD_DONE_INST,
+								 cmd_done);
 				val = BIT(INT_WAVE5_DEC_PIC);
 				kfifo_in(&inst->irq_status, &val, sizeof(int));
 			}
@@ -101,6 +94,20 @@ static void wave5_vpu_handle_irq(void *dev_id)
 	}
 	spin_unlock_irqrestore(&dev->irq_spinlock, flags);
 
+	/*
+	 * Acknowledge only now that every instance bit this interrupt carried
+	 * has been consumed. W5_RET_QUEUE_CMD_DONE_INST is written by both
+	 * sides, but the firmware does not update it, for any reason, until
+	 * the interrupt is acknowledged through W5_VPU_VINT_REASON_CLR and
+	 * W5_VPU_VINT_CLEAR. Until then the snapshot taken above stays exact
+	 * and the read-modify-write in the loop cannot lose a bit.
+	 * Acknowledging first would let the firmware add an instance bit
+	 * underneath that snapshot, and the write-back would then drop it --
+	 * an instance whose completion is never reported again.
+	 */
+	wave5_vdi_write_register(dev, W5_VPU_VINT_REASON_CLR, irq_reason);
+	wave5_vdi_write_register(dev, W5_VPU_VINT_CLEAR, 0x1);
+
 	if (dev->irq < 0)
 		up(&dev->irq_sem);
 }
-- 
2.43.0