[PATCH 2/2] media: aspeed: fix clock handling logic

[Jae Hyun Yoo]

Video engine uses eclk and vclk for its clock sources and its reset
control is coupled with eclk so the current clock enabling sequence works
like below.

 Enable eclk
 De-assert Video Engine reset
 10ms delay
 Enable vclk

It introduces improper reset on the Video Engine hardware and eventually
the hardware generates unexpected DMA memory transfers that can corrupt
memory region in random and sporadic patterns. This issue is observed
very rarely on some specific AST2500 SoCs but it causes a critical
kernel panic with making a various shape of signature so it's extremely
hard to debug. Moreover, the issue is observed even when the video
engine is not actively used because udevd turns on the video engine
hardware for a short time to make a query in every boot.

To fix this issue, this commit changes the clock handling logic to make
the reset de-assertion triggered after enabling both eclk and vclk. Also,
it adds clk_unprepare call for a case when probe fails.

Fixes: d2b4387f3bdf ("media: platform: Add Aspeed Video Engine driver")
Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo at linux.intel.com>
---
 drivers/media/platform/aspeed-video.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/media/platform/aspeed-video.c b/drivers/media/platform/aspeed-video.c
index c46a79eace98..db072ff2df70 100644
--- a/drivers/media/platform/aspeed-video.c
+++ b/drivers/media/platform/aspeed-video.c
@@ -514,8 +514,8 @@ static void aspeed_video_off(struct aspeed_video *video)
 	aspeed_video_write(video, VE_INTERRUPT_STATUS, 0xffffffff);
 
 	/* Turn off the relevant clocks */
-	clk_disable(video->vclk);
 	clk_disable(video->eclk);
+	clk_disable(video->vclk);
 
 	clear_bit(VIDEO_CLOCKS_ON, &video->flags);
 }
@@ -526,8 +526,8 @@ static void aspeed_video_on(struct aspeed_video *video)
 		return;
 
 	/* Turn on the relevant clocks */
-	clk_enable(video->eclk);
 	clk_enable(video->vclk);
+	clk_enable(video->eclk);
 
 	set_bit(VIDEO_CLOCKS_ON, &video->flags);
 }
@@ -1719,8 +1719,11 @@ static int aspeed_video_probe(struct platform_device *pdev)
 		return rc;
 
 	rc = aspeed_video_setup_video(video);
-	if (rc)
+	if (rc) {
+		clk_unprepare(video->vclk);
+		clk_unprepare(video->eclk);
 		return rc;
+	}
 
 	return 0;
 }
-- 
2.17.1