Re: [PATCH v2] media: platform: fix a kernel warning on clk control

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On 4/12/2019 5:17 AM, Herrenschmidt, Benjamin wrote:

On Fri, 2019-04-12 at 13:00 +0200, Hans Verkuil wrote:

Eddie, can you review this?

Jae Hyun Yoo, for future reference: please add the driver name in the
subject.
I.e. something like this: [PATCH v2] media: aspeed: fix a kernel
warning on clk control

That helps maintainers figuring out who should look at which patch.


test_bit/clear_bit/set_bit are atomic. The way they are used here is
either a waste of cycles (there's already a lock) or racy. Not too sure
:)


Hi Ben,

I added spin lock handling too to protect corresponding sequence of
turning on and off of the video engine which should be serialized.
Even with this protection, clock enable/disable can be double called
so I had to add the flag checking.

Thanks,
Jae


Cheers,
Ben.


Regards,

	Hans

On 3/29/19 10:27 PM, Jae Hyun Yoo wrote:

video_on and video_off functions in the Aspeed video engine driver
are
being called from multiple contexts without any protection so video
clocks
can be disabled twice and eventually it causes a kernel warning
with stack
dump printing out like below:

[  120.034729] WARNING: CPU: 0 PID: 1334 at drivers/clk/clk.c:684
clk_core_unprepare+0x13c/0x170
[  120.043252] eclk-gate already unprepared
[  120.047283] CPU: 0 PID: 1334 Comm: obmc-ikvm Tainted:
G        W         5.0.3-b94b74e8b52db91fe4e99e0bb481ec8bf2b5b47c
#1
[  120.058417] Hardware name: Generic DT based system
[  120.063219] Backtrace:
[  120.065787] [<80107cdc>] (dump_backtrace) from [<80107f10>]
(show_stack+0x20/0x24)
[  120.073371]  r7:803a4ff0 r6:00000009 r5:00000000 r4:96197e1c
[  120.079152] [<80107ef0>] (show_stack) from [<8068f7d8>]
(dump_stack+0x20/0x28)
[  120.086479] [<8068f7b8>] (dump_stack) from [<8011604c>]
(__warn.part.3+0xb4/0xdc)
[  120.094068] [<80115f98>] (__warn.part.3) from [<801160e0>]
(warn_slowpath_fmt+0x6c/0x90)
[  120.102164]  r6:000002ac r5:8080c0b8 r4:80a07008
[  120.106893] [<80116078>] (warn_slowpath_fmt) from [<803a4ff0>]
(clk_core_unprepare+0x13c/0x170)
[  120.115686]  r3:8080cf8c r2:8080c17c
[  120.119276]  r7:97d68e58 r6:9df23200 r5:9668c260 r4:96459260
[  120.125046] [<803a4eb4>] (clk_core_unprepare) from [<803a707c>]
(clk_unprepare+0x34/0x3c)
[  120.133226]  r5:9668c260 r4:96459260
[  120.136932] [<803a7048>] (clk_unprepare) from [<804f34bc>]
(aspeed_video_off+0x44/0x48)
[  120.145031]  r5:9668c260 r4:9668cbc0
[  120.148647] [<804f3478>] (aspeed_video_off) from [<804f3fd0>]
(aspeed_video_release+0x94/0x118)
[  120.157435]  r5:966a0cb8 r4:966a0800
[  120.161049] [<804f3f3c>] (aspeed_video_release) from
[<804d2c58>] (v4l2_release+0xd4/0xe8)
[  120.169404]  r7:97d68e58 r6:9d087810 r5:9df23200 r4:966a0b20
[  120.175168] [<804d2b84>] (v4l2_release) from [<80236224>]
(__fput+0x98/0x1c4)
[  120.182316]  r5:96698e78 r4:9df23200
[  120.185994] [<8023618c>] (__fput) from [<802363b8>]
(____fput+0x18/0x1c)
[  120.192712]  r9:80a0700c r8:801011e4 r7:00000000 r6:80a64bbc
r5:961dd560 r4:961dd89c
[  120.200562] [<802363a0>] (____fput) from [<80131c08>]
(task_work_run+0x7c/0xa4)
[  120.207994] [<80131b8c>] (task_work_run) from [<80106884>]
(do_work_pending+0x4a8/0x578)
[  120.216163]  r7:801011e4 r6:80a07008 r5:96197fb0 r4:ffffe000
[  120.221856] [<801063dc>] (do_work_pending) from [<8010106c>]
(slow_work_pending+0xc/0x20)
[  120.230116] Exception stack(0x96197fb0 to 0x96197ff8)
[  120.235254] 7fa0:                                     00000000
76ccf094 00000000 00000000
[  120.243438] 7fc0: 00000008 00a11978 7eab3c30 00000006 00000000
00000000 475b0fa4 00000000
[  120.251692] 7fe0: 00000002 7eab3a40 00000000 47720e38 80000010
00000008
[  120.258396]  r10:00000000 r9:96196000 r8:801011e4 r7:00000006
r6:7eab3c30 r5:00a11978
[  120.266291]  r4:00000008

To prevent this issue, this commit adds spinlock protection and
clock
status checking logic into the Aspeed video engine driver.

Fixes: d2b4387f3bdf ("media: platform: Add Aspeed Video Engine
driver")
Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo@xxxxxxxxxxxxxxx>
Cc: Eddie James <eajames@xxxxxxxxxxxxx>
Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
Cc: Joel Stanley <joel@xxxxxxxxx>
Cc: Andrew Jeffery <andrew@xxxxxxxx>
---
  drivers/media/platform/aspeed-video.c | 32
++++++++++++++++++++++++---
  1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/drivers/media/platform/aspeed-video.c
b/drivers/media/platform/aspeed-video.c
index 692e08ef38c0..744d22ecc620 100644
--- a/drivers/media/platform/aspeed-video.c
+++ b/drivers/media/platform/aspeed-video.c
@@ -188,6 +188,7 @@ enum {
  	VIDEO_STREAMING,
  	VIDEO_FRAME_INPRG,
  	VIDEO_STOPPED,
+	VIDEO_CLOCKS_ON,
  };
struct aspeed_video_addr { 
@@ -495,20 +496,30 @@ static void aspeed_video_reset(struct
aspeed_video *video)
static void aspeed_video_off(struct aspeed_video *video) 
  {
+	if (!test_bit(VIDEO_CLOCKS_ON, &video->flags))
+		return;
+
  	aspeed_video_reset(video);
/* Turn off the relevant clocks */ 
  	clk_disable_unprepare(video->vclk);
  	clk_disable_unprepare(video->eclk);
+
+	clear_bit(VIDEO_CLOCKS_ON, &video->flags);
  }
static void aspeed_video_on(struct aspeed_video *video) 
  {
+	if (test_bit(VIDEO_CLOCKS_ON, &video->flags))
+		return;
+
  	/* Turn on the relevant clocks */
  	clk_prepare_enable(video->eclk);
  	clk_prepare_enable(video->vclk);
aspeed_video_reset(video); 
+
+	set_bit(VIDEO_CLOCKS_ON, &video->flags);
  }
static void aspeed_video_bufs_done(struct aspeed_video *video, 
@@ -526,12 +537,14 @@ static void aspeed_video_bufs_done(struct
aspeed_video *video,
static void aspeed_video_irq_res_change(struct aspeed_video 
*video)
  {
+	spin_lock(&video->lock);
  	dev_dbg(video->dev, "Resolution changed; resetting\n");
set_bit(VIDEO_RES_CHANGE, &video->flags); 
  	clear_bit(VIDEO_FRAME_INPRG, &video->flags);
aspeed_video_off(video); 
+	spin_unlock(&video->lock);
  	aspeed_video_bufs_done(video, VB2_BUF_STATE_ERROR);
schedule_delayed_work(&video->res_work, 
RESOLUTION_CHANGE_DELAY);
@@ -951,9 +964,13 @@ static void aspeed_video_init_regs(struct
aspeed_video *video)
static void aspeed_video_start(struct aspeed_video *video) 
  {
+	unsigned long flags;
+
+	spin_lock_irqsave(&video->lock, flags);
  	aspeed_video_on(video);
aspeed_video_init_regs(video); 
+	spin_unlock_irqrestore(&video->lock, flags);
/* Resolution set to 640x480 if no signal found */ 
  	aspeed_video_get_resolution(video);
@@ -969,6 +986,9 @@ static void aspeed_video_start(struct
aspeed_video *video)
static void aspeed_video_stop(struct aspeed_video *video) 
  {
+	unsigned long flags;
+
+	spin_lock_irqsave(&video->lock, flags);
  	set_bit(VIDEO_STOPPED, &video->flags);
  	cancel_delayed_work_sync(&video->res_work);
@@ -982,6 +1002,7 @@ static void aspeed_video_stop(struct 
aspeed_video *video)
video->v4l2_input_status = V4L2_IN_ST_NO_SIGNAL; 
  	video->flags = 0;
+	spin_unlock_irqrestore(&video->lock, flags);
  }
static int aspeed_video_querycap(struct file *file, void *fh, 
@@ -1319,16 +1340,21 @@ static void
aspeed_video_resolution_work(struct work_struct *work)
  	struct delayed_work *dwork = to_delayed_work(work);
  	struct aspeed_video *video = container_of(dwork, struct
aspeed_video,
  						  res_work);
-	u32 input_status = video->v4l2_input_status;
+	unsigned long flags;
+	u32 input_status;
+ spin_lock_irqsave(&video->lock, flags); 
+	input_status = video->v4l2_input_status;
  	aspeed_video_on(video);
/* Exit early in case no clients remain */ 
-	if (test_bit(VIDEO_STOPPED, &video->flags))
+	if (test_bit(VIDEO_STOPPED, &video->flags)) {
+		spin_unlock_irqrestore(&video->lock, flags);
  		goto done;
+	}
aspeed_video_init_regs(video); 
-
+	spin_unlock_irqrestore(&video->lock, flags);
  	aspeed_video_get_resolution(video);
if (video->detected_timings.width != video- 
active_timings.width ||
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