linux-kernel - Re: [PATCH 58/78] media: exynos-gsc: use pm_runtime_resume_and

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Message-ID: <20210428091302.64af1e5d@coco.lan>
Date:   Wed, 28 Apr 2021 09:13:02 +0200
From:   Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To:     Sylwester Nawrocki <s.nawrocki@...sung.com>
Cc:     linuxarm@...wei.com, mauro.chehab@...wei.com,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH 58/78] media: exynos-gsc: use
 pm_runtime_resume_and_get()

Em Tue, 27 Apr 2021 13:50:44 +0200
Sylwester Nawrocki <s.nawrocki@...sung.com> escreveu:

> On 27.04.2021 11:42, Mauro Carvalho Chehab wrote:
> > Em Tue, 27 Apr 2021 11:30:55 +0200
> > Mauro Carvalho Chehab <mchehab+huawei@...nel.org> escreveu:
> >   
> >> Em Tue, 27 Apr 2021 10:18:12 +0200
> >> Sylwester Nawrocki <s.nawrocki@...sung.com> escreveu:
> >>  
> >>> On 24.04.2021 08:45, 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/platform/exynos-gsc/gsc-core.c | 3 +--
> >>>>  drivers/media/platform/exynos-gsc/gsc-m2m.c  | 2 +-
> >>>>  2 files changed, 2 insertions(+), 3 deletions(-)
> >>>>
> >>>> diff --git a/drivers/media/platform/exynos-gsc/gsc-core.c b/drivers/media/platform/exynos-gsc/gsc-core.c
> >>>> index 9f41c2e7097a..9d5841194f6b 100644
> >>>> --- a/drivers/media/platform/exynos-gsc/gsc-core.c
> >>>> +++ b/drivers/media/platform/exynos-gsc/gsc-core.c
> >>>> @@ -1210,7 +1210,7 @@ static int gsc_remove(struct platform_device *pdev)
> >>>>  	struct gsc_dev *gsc = platform_get_drvdata(pdev);
> >>>>  	int i;
> >>>>  
> >>>> -	pm_runtime_get_sync(&pdev->dev);
> >>>> +	pm_runtime_resume_and_get(&pdev->dev);
> >>>>  
> >>>>  	gsc_unregister_m2m_device(gsc);
> >>>>  	v4l2_device_unregister(&gsc->v4l2_dev);
> >>>> @@ -1219,7 +1219,6 @@ static int gsc_remove(struct platform_device *pdev)
> >>>>  	for (i = 0; i < gsc->num_clocks; i++)
> >>>>  		clk_disable_unprepare(gsc->clock[i]);
> >>>>  
> >>>> -	pm_runtime_put_noidle(&pdev->dev);      
> >>>
> >>> If we do this then the device usage count will not get decremented
> >>> after the pm_runtime_resume_and_get() call above and after driver
> >>> unload/load cycle it will not be possible to suspend the device.
> >>> I wouldn't be changing anything in gsc_remove(), pm_runtime_get_sync()
> >>> works better in that case.    
> >>
> >> Good point.
> >>
> >> Actually, I don't see any reason why to call a PM resume
> >> function - either being pm_runtime_get_sync() or
> >> pm_runtime_resume_and_get().
> >>
> >> The code there could simply be:
> >>
> >>     static int gsc_remove(struct platform_device *pdev)
> >>     {
> >>         struct gsc_dev *gsc = platform_get_drvdata(pdev);
> >>         int i;
> >>
> >>         gsc_unregister_m2m_device(gsc);
> >>         v4l2_device_unregister(&gsc->v4l2_dev);
> >>
> >>         vb2_dma_contig_clear_max_seg_size(&pdev->dev);
> >>         for (i = 0; i < gsc->num_clocks; i++)
> >>                 clk_disable_unprepare(gsc->clock[i]);
> >>
> >>         pm_runtime_disable(&pdev->dev);
> >>
> >>         dev_dbg(&pdev->dev, "%s driver unloaded\n", pdev->name);
> >>         return 0;
> >>     }
> >>
> >> Eventually also adding:
> >> 	pm_runtime_suspended(&pdev->dev);  
> > 
> > In time: I actually meant:
> > 
> > 	pm_runtime_set_suspended(&pdev->dev);
> > 
> > but after double-checking the PM runtime code, it sounds to me that
> > just calling pm_runtime_disable() would be enough. Not 100% sure
> > here. Btw, some media drivers call it after pm_runtime_disable(),
> > while others don't do.  
> 
> I think if the device is brought into suspended state (e.g. by
> disabling clocks as above) the pm_runtime_set_suspended() call
> should be there. IOW a following sequence: 
> 
> 	pm_runtime_disable(dev);
> 	if (!pm_runtime_status_suspended(dev))
> 		/* put device into suspended state (disable clocks, 
> 		  voltage regulators, assert GPIOs, etc. */
> 	pm_runtime_set_suspended(dev);

Not sure if this would work, as the clock framework would try
to do things like calling clk_pm_runtime_put().

Perhaps an alternative would be to just return an error if it
can't resume PM runtime, e. g.:

diff --git a/drivers/media/platform/exynos-gsc/gsc-core.c b/drivers/media/platform/exynos-gsc/gsc-core.c
index 9f41c2e7097a..d47d02c75484 100644
--- a/drivers/media/platform/exynos-gsc/gsc-core.c
+++ b/drivers/media/platform/exynos-gsc/gsc-core.c
@@ -1208,9 +1208,11 @@ static int gsc_probe(struct platform_device *pdev)
 static int gsc_remove(struct platform_device *pdev)
 {
        struct gsc_dev *gsc = platform_get_drvdata(pdev);
-       int i;
+       int ret, i;
 
-       pm_runtime_get_sync(&pdev->dev);
+       ret = pm_runtime_resume_and_get(&pdev->dev);
+       if (ret < 0)
+               return ret;
 
        gsc_unregister_m2m_device(gsc);
        v4l2_device_unregister(&gsc->v4l2_dev);


Thanks,
Mauro