linux-kernel - Re: [PATCH 25/78] media: i2c: ccs-core: use pm_runtime_resume_and

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Date:   Mon, 26 Apr 2021 16:01:51 +0200
From:   Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     linuxarm@...wei.com, mauro.chehab@...wei.com,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org
Subject: Re: [PATCH 25/78] media: i2c: ccs-core: use
 pm_runtime_resume_and_get()

Em Sun, 25 Apr 2021 21:55:25 +0300
Sakari Ailus <sakari.ailus@...ux.intel.com> escreveu:

> Hi Mauro,
> 
> Thanks for the patch.
> 
> On Sat, Apr 24, 2021 at 08:44:35AM +0200, Mauro Carvalho Chehab wrote:
> > 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.
> > 
> > Use the new API, in order to cleanup the error check logic.
> > 
> > Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
> > ---
> >  drivers/media/i2c/ccs/ccs-core.c | 11 +++++------
> >  1 file changed, 5 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/media/i2c/ccs/ccs-core.c b/drivers/media/i2c/ccs/ccs-core.c
> > index 9dc3f45da3dc..1441ddcc9b35 100644
> > --- a/drivers/media/i2c/ccs/ccs-core.c
> > +++ b/drivers/media/i2c/ccs/ccs-core.c
> > @@ -1880,12 +1880,11 @@ static int ccs_pm_get_init(struct ccs_sensor *sensor)
> >  	struct i2c_client *client = v4l2_get_subdevdata(&sensor->src->sd);
> >  	int rval;
> >  
> > -	rval = pm_runtime_get_sync(&client->dev);
> > -	if (rval < 0) {
> > -		pm_runtime_put_noidle(&client->dev);
> > -
> > +	rval = pm_runtime_resume_and_get(&client->dev);
> > +	if (rval < 0)
> >  		return rval;
> > -	} else if (!rval) {
> > +
> > +	if (!rval) {
> >  		rval = v4l2_ctrl_handler_setup(&sensor->pixel_array->
> >  					       ctrl_handler);
> >  		if (rval)
> > @@ -3089,7 +3088,7 @@ static int __maybe_unused ccs_suspend(struct device *dev)
> >  	bool streaming = sensor->streaming;
> >  	int rval;
> >  
> > -	rval = pm_runtime_get_sync(dev);
> > +	rval = pm_runtime_resume_and_get(dev);
> >  	if (rval < 0) {
> >  		pm_runtime_put_noidle(dev);  
> 
> You'll need to drop pm_runtime_put_noidle() here.

OK!

---

On a non-related issue at the same code, after the change, the
suspend function will be:

  static int __maybe_unused ccs_suspend(struct device *dev)
  {
        struct i2c_client *client = to_i2c_client(dev);
        struct v4l2_subdev *subdev = i2c_get_clientdata(client);
        struct ccs_sensor *sensor = to_ccs_sensor(subdev);
        bool streaming = sensor->streaming;
        int rval;

        rval = pm_runtime_resume_and_get(dev);
        if (rval < 0) 
                return -EAGAIN;

        if (sensor->streaming)
                ccs_stop_streaming(sensor);

        /* save state for resume */
        sensor->streaming = streaming;

        return 0;
  }

Not sure if "return -EAGAIN" is the right thing here. I mean,
the PM runtime core has two error conditions that are independent
on whatever the PM callback would be doing[1]:

	        if (dev->power.runtime_error)
                retval = -EINVAL;
        else if (dev->power.disable_depth > 0)
                retval = -EACCES;

It would be very unlikely that trying to suspend again would solve
those conditions.

So, I guess that the right thing to do is to change the code
to do, instead:

  static int __maybe_unused ccs_suspend(struct device *dev)
  {
        struct i2c_client *client = to_i2c_client(dev);
        struct v4l2_subdev *subdev = i2c_get_clientdata(client);
        struct ccs_sensor *sensor = to_ccs_sensor(subdev);
        bool streaming = sensor->streaming;
        int rval;

        rval = pm_runtime_resume_and_get(dev);
        if (rval < 0) 
                return rval;
	...
  }


[1] see rpm_resume() code at drivers/base/power/runtime.c.

Thanks,
Mauro