[PATCH] drm/msm/dp: do not complete dp_aux_cmd_fifo_tx() if irq is not for aux transfer

[Kuogee Hsieh]

There are 3 possible interrupt sources are handled by DP controller,
HPDstatus, Controller state changes and Aux read/write transaction.
At every irq, DP controller have to check isr status of every interrupt
sources and service the interrupt if its isr status bits shows interrupts
are pending. There is potential race condition may happen at current aux
isr handler implementation since it is always complete dp_aux_cmd_fifo_tx()
even irq is not for aux read or write transaction. This may cause aux read
transaction return premature if host aux data read is in the middle of
waiting for sink to complete transferring data to host while irq happen.
This will cause host's receiving buffer contains unexpected data. This
patch fixes this problem by checking aux isr and return immediately at
aux isr handler if there are no any isr status bits set.

Follows are the signature at kernel logs when problem happen,
EDID has corrupt header
panel-simple-dp-aux aux-aea0000.edp: Couldn't identify panel via EDID
panel-simple-dp-aux aux-aea0000.edp: error -EIO: Couldn't detect panel nor find a fallback

Signed-off-by: Kuogee Hsieh <quic_khsieh@xxxxxxxxxxx>
---
 drivers/gpu/drm/msm/dp/dp_aux.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/msm/dp/dp_aux.c b/drivers/gpu/drm/msm/dp/dp_aux.c
index d030a93..8f8b12a 100644
--- a/drivers/gpu/drm/msm/dp/dp_aux.c
+++ b/drivers/gpu/drm/msm/dp/dp_aux.c
@@ -423,6 +423,13 @@ void dp_aux_isr(struct drm_dp_aux *dp_aux)
 
 	isr = dp_catalog_aux_get_irq(aux->catalog);
 
+	/*
+	 * if this irq is not for aux transfer,
+	 * then return immediately
+	 */
+	if (!isr)
+		return;
+
 	if (!aux->cmd_busy)
 		return;
 
-- 
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