[PATCH] media: sunxi: sun6i_mipi_csi2.c/sun8i_a83t_mipi_csi2.c: clarify error handling

[PATCH] media: sunxi: sun6i_mipi_csi2.c/sun8i_a83t_mipi_csi2.c: clarify error handling

[Hans Verkuil]

Both sun6i_mipi_csi2.c and sun8i_a83t_mipi_csi2.c have the same issue:
the comment before the ret = 0 assignment is incorrect, drop it and
always assign the result of the v4l2_subdev_call(..., 0) to ret.

In the disable label check for !on and set ret to 0 in that case.

This fixes two smatch warnings:

drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c:193 sun6i_mipi_csi2_s_stream() warn: missing error code 'ret'
drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c:225 sun8i_a83t_mipi_csi2_s_stream() warn: missing error code 'ret'

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
---
 .../media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c | 7 ++++---
 .../sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c      | 7 ++++---
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c b/drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c
index 31e12f1506cb..a4e3f9a6b2ff 100644
--- a/drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c
+++ b/drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c
@@ -182,14 +182,13 @@ static int sun6i_mipi_csi2_s_stream(struct v4l2_subdev *subdev, int on)
 	unsigned int lanes_count =
 		csi2_dev->bridge.endpoint.bus.mipi_csi2.num_data_lanes;
 	unsigned long pixel_rate;
-	/* Initialize to 0 to use both in disable label (ret != 0) and off. */
-	int ret = 0;
+	int ret;
 
 	if (!source_subdev)
 		return -ENODEV;
 
 	if (!on) {
-		v4l2_subdev_call(source_subdev, video, s_stream, 0);
+		ret = v4l2_subdev_call(source_subdev, video, s_stream, 0);
 		goto disable;
 	}
 
@@ -281,6 +280,8 @@ static int sun6i_mipi_csi2_s_stream(struct v4l2_subdev *subdev, int on)
 	return 0;
 
 disable:
+	if (!on)
+		ret = 0;
 	phy_power_off(dphy);
 	sun6i_mipi_csi2_disable(csi2_dev);
 
diff --git a/drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c b/drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c
index c82ede3ca0ff..d052ee77ef0a 100644
--- a/drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c
+++ b/drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c
@@ -214,14 +214,13 @@ static int sun8i_a83t_mipi_csi2_s_stream(struct v4l2_subdev *subdev, int on)
 	unsigned int lanes_count =
 		csi2_dev->bridge.endpoint.bus.mipi_csi2.num_data_lanes;
 	unsigned long pixel_rate;
-	/* Initialize to 0 to use both in disable label (ret != 0) and off. */
-	int ret = 0;
+	int ret;
 
 	if (!source_subdev)
 		return -ENODEV;
 
 	if (!on) {
-		v4l2_subdev_call(source_subdev, video, s_stream, 0);
+		ret = v4l2_subdev_call(source_subdev, video, s_stream, 0);
 		goto disable;
 	}
 
@@ -313,6 +312,8 @@ static int sun8i_a83t_mipi_csi2_s_stream(struct v4l2_subdev *subdev, int on)
 	return 0;
 
 disable:
+	if (!on)
+		ret = 0;
 	phy_power_off(dphy);
 	sun8i_a83t_mipi_csi2_disable(csi2_dev);
 
-- 
2.35.1

Re: [PATCH] media: sunxi: sun6i_mipi_csi2.c/sun8i_a83t_mipi_csi2.c: clarify error handling

[Paul Kocialkowski]

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Hi Hans,

On Mon 18 Jul 22, 18:08, Hans Verkuil wrote:
> Both sun6i_mipi_csi2.c and sun8i_a83t_mipi_csi2.c have the same issue:
> the comment before the ret = 0 assignment is incorrect, drop it and
> always assign the result of the v4l2_subdev_call(..., 0) to ret.

Not sure what is incorrect about it. I agree that it's good to return the
return code of v4l2_subdev_call instead of always 0 on the !on path though.

> In the disable label check for !on and set ret to 0 in that case.
> 
> This fixes two smatch warnings:
> 
> drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c:193 sun6i_mipi_csi2_s_stream() warn: missing error code 'ret'

I don't think this is legit: the initialization of ret is specifically there
to avoid an undefined ret there.

> drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c:225 sun8i_a83t_mipi_csi2_s_stream() warn: missing error code 'ret'
> 
> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> ---
>  .../media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c | 7 ++++---
>  .../sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c      | 7 ++++---
>  2 files changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c b/drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c
> index 31e12f1506cb..a4e3f9a6b2ff 100644
> --- a/drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c
> +++ b/drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c
> @@ -182,14 +182,13 @@ static int sun6i_mipi_csi2_s_stream(struct v4l2_subdev *subdev, int on)
>  	unsigned int lanes_count =
>  		csi2_dev->bridge.endpoint.bus.mipi_csi2.num_data_lanes;
>  	unsigned long pixel_rate;
> -	/* Initialize to 0 to use both in disable label (ret != 0) and off. */
> -	int ret = 0;
> +	int ret;
>  
>  	if (!source_subdev)
>  		return -ENODEV;
>  
>  	if (!on) {
> -		v4l2_subdev_call(source_subdev, video, s_stream, 0);
> +		ret = v4l2_subdev_call(source_subdev, video, s_stream, 0);
>  		goto disable;
>  	}
>  
> @@ -281,6 +280,8 @@ static int sun6i_mipi_csi2_s_stream(struct v4l2_subdev *subdev, int on)
>  	return 0;
>  
>  disable:
> +	if (!on)
> +		ret = 0;

Then this will always overwrite the ret value from v4l2_subdev_call with the
!on disable path. Looks like this can be removed.

What do you think?

Paul

>  	phy_power_off(dphy);
>  	sun6i_mipi_csi2_disable(csi2_dev);
>  
> diff --git a/drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c b/drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c
> index c82ede3ca0ff..d052ee77ef0a 100644
> --- a/drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c
> +++ b/drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c
> @@ -214,14 +214,13 @@ static int sun8i_a83t_mipi_csi2_s_stream(struct v4l2_subdev *subdev, int on)
>  	unsigned int lanes_count =
>  		csi2_dev->bridge.endpoint.bus.mipi_csi2.num_data_lanes;
>  	unsigned long pixel_rate;
> -	/* Initialize to 0 to use both in disable label (ret != 0) and off. */
> -	int ret = 0;
> +	int ret;
>  
>  	if (!source_subdev)
>  		return -ENODEV;
>  
>  	if (!on) {
> -		v4l2_subdev_call(source_subdev, video, s_stream, 0);
> +		ret = v4l2_subdev_call(source_subdev, video, s_stream, 0);
>  		goto disable;
>  	}
>  
> @@ -313,6 +312,8 @@ static int sun8i_a83t_mipi_csi2_s_stream(struct v4l2_subdev *subdev, int on)
>  	return 0;
>  
>  disable:
> +	if (!on)
> +		ret = 0;
>  	phy_power_off(dphy);
>  	sun8i_a83t_mipi_csi2_disable(csi2_dev);
>  
> -- 
> 2.35.1
> 

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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Re: [PATCH] media: sunxi: sun6i_mipi_csi2.c/sun8i_a83t_mipi_csi2.c: clarify error handling

[Hans Verkuil]

On 7/19/22 11:54, Paul Kocialkowski wrote:
> Hi Hans,
> 
> On Mon 18 Jul 22, 18:08, Hans Verkuil wrote:
>> Both sun6i_mipi_csi2.c and sun8i_a83t_mipi_csi2.c have the same issue:
>> the comment before the ret = 0 assignment is incorrect, drop it and
>> always assign the result of the v4l2_subdev_call(..., 0) to ret.
> 
> Not sure what is incorrect about it. I agree that it's good to return the
> return code of v4l2_subdev_call instead of always 0 on the !on path though.
> 
>> In the disable label check for !on and set ret to 0 in that case.
>>
>> This fixes two smatch warnings:
>>
>> drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c:193 sun6i_mipi_csi2_s_stream() warn: missing error code 'ret'
> 
> I don't think this is legit: the initialization of ret is specifically there
> to avoid an undefined ret there.

I believe so as well, but I need to get rid of the smatch warning.

> 
>> drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c:225 sun8i_a83t_mipi_csi2_s_stream() warn: missing error code 'ret'
>>
>> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
>> ---
>>  .../media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c | 7 ++++---
>>  .../sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c      | 7 ++++---
>>  2 files changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c b/drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c
>> index 31e12f1506cb..a4e3f9a6b2ff 100644
>> --- a/drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c
>> +++ b/drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c
>> @@ -182,14 +182,13 @@ static int sun6i_mipi_csi2_s_stream(struct v4l2_subdev *subdev, int on)
>>  	unsigned int lanes_count =
>>  		csi2_dev->bridge.endpoint.bus.mipi_csi2.num_data_lanes;
>>  	unsigned long pixel_rate;
>> -	/* Initialize to 0 to use both in disable label (ret != 0) and off. */
>> -	int ret = 0;
>> +	int ret;
>>  
>>  	if (!source_subdev)
>>  		return -ENODEV;
>>  
>>  	if (!on) {
>> -		v4l2_subdev_call(source_subdev, video, s_stream, 0);
>> +		ret = v4l2_subdev_call(source_subdev, video, s_stream, 0);
>>  		goto disable;
>>  	}
>>  
>> @@ -281,6 +280,8 @@ static int sun6i_mipi_csi2_s_stream(struct v4l2_subdev *subdev, int on)
>>  	return 0;
>>  
>>  disable:
>> +	if (!on)
>> +		ret = 0;
> 
> Then this will always overwrite the ret value from v4l2_subdev_call with the
> !on disable path. Looks like this can be removed.

Returning an error when stopping streaming is kind of pointless, since
what are you going to do with that error?

I assumed that's why the original code did this, and I didn't want to
change the behavior.

If you think it is better to just return the error, then that can be a
patch on top.

BTW, I think it would have been better to have separate streamon and streamoff
ops instead of a single s_stream. Starting streaming would return an int, while
stopping streaming would be a void function. In general when you stop, release,
close, etc. something there is no point in an error code since there is nothing
you can do with it.

Regards,

	Hans

> 
> What do you think?
> 
> Paul
> 
>>  	phy_power_off(dphy);
>>  	sun6i_mipi_csi2_disable(csi2_dev);
>>  
>> diff --git a/drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c b/drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c
>> index c82ede3ca0ff..d052ee77ef0a 100644
>> --- a/drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c
>> +++ b/drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c
>> @@ -214,14 +214,13 @@ static int sun8i_a83t_mipi_csi2_s_stream(struct v4l2_subdev *subdev, int on)
>>  	unsigned int lanes_count =
>>  		csi2_dev->bridge.endpoint.bus.mipi_csi2.num_data_lanes;
>>  	unsigned long pixel_rate;
>> -	/* Initialize to 0 to use both in disable label (ret != 0) and off. */
>> -	int ret = 0;
>> +	int ret;
>>  
>>  	if (!source_subdev)
>>  		return -ENODEV;
>>  
>>  	if (!on) {
>> -		v4l2_subdev_call(source_subdev, video, s_stream, 0);
>> +		ret = v4l2_subdev_call(source_subdev, video, s_stream, 0);
>>  		goto disable;
>>  	}
>>  
>> @@ -313,6 +312,8 @@ static int sun8i_a83t_mipi_csi2_s_stream(struct v4l2_subdev *subdev, int on)
>>  	return 0;
>>  
>>  disable:
>> +	if (!on)
>> +		ret = 0;
>>  	phy_power_off(dphy);
>>  	sun8i_a83t_mipi_csi2_disable(csi2_dev);
>>  
>> -- 
>> 2.35.1
>>
> 

Re: [PATCH] media: sunxi: sun6i_mipi_csi2.c/sun8i_a83t_mipi_csi2.c: clarify error handling

[Paul Kocialkowski]

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Hans,

On Tue 19 Jul 22, 12:04, Hans Verkuil wrote:
> On 7/19/22 11:54, Paul Kocialkowski wrote:
> > Hi Hans,
> > 
> > On Mon 18 Jul 22, 18:08, Hans Verkuil wrote:
> >> Both sun6i_mipi_csi2.c and sun8i_a83t_mipi_csi2.c have the same issue:
> >> the comment before the ret = 0 assignment is incorrect, drop it and
> >> always assign the result of the v4l2_subdev_call(..., 0) to ret.
> > 
> > Not sure what is incorrect about it. I agree that it's good to return the
> > return code of v4l2_subdev_call instead of always 0 on the !on path though.
> > 
> >> In the disable label check for !on and set ret to 0 in that case.
> >>
> >> This fixes two smatch warnings:
> >>
> >> drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c:193 sun6i_mipi_csi2_s_stream() warn: missing error code 'ret'
> > 
> > I don't think this is legit: the initialization of ret is specifically there
> > to avoid an undefined ret there.
> 
> I believe so as well, but I need to get rid of the smatch warning.

Yes fair enough, I was just a bit confused by the commit message.

> >> drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c:225 sun8i_a83t_mipi_csi2_s_stream() warn: missing error code 'ret'
> >>
> >> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> >> ---
> >>  .../media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c | 7 ++++---
> >>  .../sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c      | 7 ++++---
> >>  2 files changed, 8 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c b/drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c
> >> index 31e12f1506cb..a4e3f9a6b2ff 100644
> >> --- a/drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c
> >> +++ b/drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c
> >> @@ -182,14 +182,13 @@ static int sun6i_mipi_csi2_s_stream(struct v4l2_subdev *subdev, int on)
> >>  	unsigned int lanes_count =
> >>  		csi2_dev->bridge.endpoint.bus.mipi_csi2.num_data_lanes;
> >>  	unsigned long pixel_rate;
> >> -	/* Initialize to 0 to use both in disable label (ret != 0) and off. */
> >> -	int ret = 0;
> >> +	int ret;
> >>  
> >>  	if (!source_subdev)
> >>  		return -ENODEV;
> >>  
> >>  	if (!on) {
> >> -		v4l2_subdev_call(source_subdev, video, s_stream, 0);
> >> +		ret = v4l2_subdev_call(source_subdev, video, s_stream, 0);
> >>  		goto disable;
> >>  	}
> >>  
> >> @@ -281,6 +280,8 @@ static int sun6i_mipi_csi2_s_stream(struct v4l2_subdev *subdev, int on)
> >>  	return 0;
> >>  
> >>  disable:
> >> +	if (!on)
> >> +		ret = 0;
> > 
> > Then this will always overwrite the ret value from v4l2_subdev_call with the
> > !on disable path. Looks like this can be removed.
> 
> Returning an error when stopping streaming is kind of pointless, since
> what are you going to do with that error?

Yeah that's true and it's probably safer to pretend that things went well
just in case returning != 0 somehow ends up halting the turn-off sequence.

> I assumed that's why the original code did this, and I didn't want to
> change the behavior.

Yeah I think it was my initial intent to discard the v4l2_subdev_call return
code for this reason.

> If you think it is better to just return the error, then that can be a
> patch on top.

Nah I'm fine with returning zero after all. But instead of assigning ret from
v4l2_subdev_call and then overwriting it conditionally in the disable label,
you could just as well set ret = 0; before goto disable; which seems less
confusing to me. I think this should also satisfy the smatch warning.

Otherwise it would be nice to at least have a comment about it or to reflect
the ret overwrite in the commit message (and maybe add a blank like after the
conditional block while at it).

> BTW, I think it would have been better to have separate streamon and streamoff
> ops instead of a single s_stream. Starting streaming would return an int, while
> stopping streaming would be a void function. In general when you stop, release,
> close, etc. something there is no point in an error code since there is nothing
> you can do with it.

Agreed, maybe this can be somehow helpful in sensor drivers where you just have
one common bit to start/halt the stream but for more complex subdevs it's not
very helpful to have a single op.

Cheers,

Paul

> Regards,
> 
> 	Hans
> 
> > 
> > What do you think?
> > 
> > Paul
> > 
> >>  	phy_power_off(dphy);
> >>  	sun6i_mipi_csi2_disable(csi2_dev);
> >>  
> >> diff --git a/drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c b/drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c
> >> index c82ede3ca0ff..d052ee77ef0a 100644
> >> --- a/drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c
> >> +++ b/drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c
> >> @@ -214,14 +214,13 @@ static int sun8i_a83t_mipi_csi2_s_stream(struct v4l2_subdev *subdev, int on)
> >>  	unsigned int lanes_count =
> >>  		csi2_dev->bridge.endpoint.bus.mipi_csi2.num_data_lanes;
> >>  	unsigned long pixel_rate;
> >> -	/* Initialize to 0 to use both in disable label (ret != 0) and off. */
> >> -	int ret = 0;
> >> +	int ret;
> >>  
> >>  	if (!source_subdev)
> >>  		return -ENODEV;
> >>  
> >>  	if (!on) {
> >> -		v4l2_subdev_call(source_subdev, video, s_stream, 0);
> >> +		ret = v4l2_subdev_call(source_subdev, video, s_stream, 0);
> >>  		goto disable;
> >>  	}
> >>  
> >> @@ -313,6 +312,8 @@ static int sun8i_a83t_mipi_csi2_s_stream(struct v4l2_subdev *subdev, int on)
> >>  	return 0;
> >>  
> >>  disable:
> >> +	if (!on)
> >> +		ret = 0;
> >>  	phy_power_off(dphy);
> >>  	sun8i_a83t_mipi_csi2_disable(csi2_dev);
> >>  
> >> -- 
> >> 2.35.1
> >>
> > 

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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