Re: [PATCH 06/25] media: i2c: imx334: fix the pm runtime get logic

[Mauro Carvalho Chehab <mchehab+huawei@kernel.org>]

Em Wed, 5 May 2021 12:10:40 +0100
Jonathan Cameron <Jonathan.Cameron@Huawei.com> escreveu:

> On Wed, 5 May 2021 11:41:56 +0200
> Mauro Carvalho Chehab <mchehab+huawei@kernel.org> wrote:
> 
> > The PM runtime get logic is currently broken, as it checks if
> > ret is zero instead of checking if it is an error code,
> > as reported by Dan Carpenter.
> > 
> > While here, use the pm_runtime_resume_and_get() as added by:
> > commit dd8088d5a896 ("PM: runtime: Add pm_runtime_resume_and_get to deal with usage counter")
> > added pm_runtime_resume_and_get() in order to automatically handle
> > dev->power.usage_count decrement on errors. As a bonus, such function
> > always return zero on success.
> > 
> > It should also be noticed that a fail of pm_runtime_get_sync() would
> > potentially result in a spurious runtime_suspend(), instead of
> > using pm_runtime_put_noidle().  
> 
> Irony here is that pm_runtime_resume_and_get() returns <= 0 so with that
> function change, you can stick with if (ret) and still be correct.
> 
> So only one of the two changes is needed to fix the bug.

Yeah, I noticed ;-)

On media, almost all devices have I2C bus(es), and I2C send/receive functions
return positive values. So, a good practice is to check for errors with:

	if (ret < 0)

That's why I opted to keep both changes here ;-)

Regards,
Mauro

> 
> J
> > 
> > Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> > Reviewed-by: Daniele Alessandrelli <daniele.alessandrelli@intel.com>
> > Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
> > ---
> >  drivers/media/i2c/imx334.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/media/i2c/imx334.c b/drivers/media/i2c/imx334.c
> > index 047aa7658d21..23f28606e570 100644
> > --- a/drivers/media/i2c/imx334.c
> > +++ b/drivers/media/i2c/imx334.c
> > @@ -717,9 +717,9 @@ static int imx334_set_stream(struct v4l2_subdev *sd, int enable)
> >  	}
> >  
> >  	if (enable) {
> > -		ret = pm_runtime_get_sync(imx334->dev);
> > -		if (ret)
> > -			goto error_power_off;
> > +		ret = pm_runtime_resume_and_get(imx334->dev);
> > +		if (ret < 0)
> > +			goto error_unlock;
> >  
> >  		ret = imx334_start_streaming(imx334);
> >  		if (ret)
> > @@ -737,6 +737,7 @@ static int imx334_set_stream(struct v4l2_subdev *sd, int enable)
> >  
> >  error_power_off:
> >  	pm_runtime_put(imx334->dev);
> > +error_unlock:
> >  	mutex_unlock(&imx334->mutex);
> >  
> >  	return ret;  
> 



Thanks,
Mauro