linux-kernel - Re: [PATCH 17/78] staging: media: vde: use pm_runtime_resume_and

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Message-ID: <20210427112250.5d40c4f4@coco.lan>
Date:   Tue, 27 Apr 2021 11:22:50 +0200
From:   Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     linuxarm@...wei.com, mauro.chehab@...wei.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH 17/78] staging: media: vde: use
 pm_runtime_resume_and_get()

Hi Dmitry,

Em Sat, 24 Apr 2021 10:35:22 +0300
Dmitry Osipenko <digetx@...il.com> escreveu:

> 24.04.2021 09:44, Mauro Carvalho Chehab пишет:
> > 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/staging/media/tegra-vde/vde.c | 16 ++++++++++------
> >  1 file changed, 10 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/staging/media/tegra-vde/vde.c b/drivers/staging/media/tegra-vde/vde.c
> > index 28845b5bafaf..8936f140a246 100644
> > --- a/drivers/staging/media/tegra-vde/vde.c
> > +++ b/drivers/staging/media/tegra-vde/vde.c
> > @@ -775,9 +775,9 @@ static int tegra_vde_ioctl_decode_h264(struct tegra_vde *vde,
> >  	if (ret)
> >  		goto release_dpb_frames;
> >  
> > -	ret = pm_runtime_get_sync(dev);
> > +	ret = pm_runtime_resume_and_get(dev);
> >  	if (ret < 0)
> > -		goto put_runtime_pm;
> > +		goto unlock;
> >  
> >  	/*
> >  	 * We rely on the VDE registers reset value, otherwise VDE
> > @@ -843,6 +843,8 @@ static int tegra_vde_ioctl_decode_h264(struct tegra_vde *vde,
> >  put_runtime_pm:
> >  	pm_runtime_mark_last_busy(dev);
> >  	pm_runtime_put_autosuspend(dev);
> > +
> > +unlock:
> >  	mutex_unlock(&vde->lock);
> >  
> >  release_dpb_frames:
> > @@ -1069,8 +1071,8 @@ static int tegra_vde_probe(struct platform_device *pdev)
> >  	 * power-cycle it in order to put hardware into a predictable lower
> >  	 * power state.
> >  	 */
> > -	pm_runtime_get_sync(dev);
> > -	pm_runtime_put(dev);
> > +	if (pm_runtime_resume_and_get(dev) >= 0)
> > +		pm_runtime_put(dev);
> >  
> >  	return 0;
> >  
> > @@ -1088,8 +1090,9 @@ static int tegra_vde_remove(struct platform_device *pdev)
> >  {
> >  	struct tegra_vde *vde = platform_get_drvdata(pdev);
> >  	struct device *dev = &pdev->dev;
> > +	int ret;
> >  
> > -	pm_runtime_get_sync(dev);
> > +	ret = pm_runtime_resume_and_get(dev);
> >  	pm_runtime_dont_use_autosuspend(dev);
> >  	pm_runtime_disable(dev);
> >  
> > @@ -1097,7 +1100,8 @@ static int tegra_vde_remove(struct platform_device *pdev)
> >  	 * Balance RPM state, the VDE power domain is left ON and hardware
> >  	 * is clock-gated. It's safe to reboot machine now.
> >  	 */
> > -	pm_runtime_put_noidle(dev);
> > +	if (ret >= 0)
> > +		pm_runtime_put_noidle(dev);
> >  	clk_disable_unprepare(vde->clk);
> >  
> >  	misc_deregister(&vde->miscdev);
> >   
> 
> Hello Mauro,
> 
> Thank you very much for the patch. It looks to me that the original
> variant was a bit simpler, this patch adds more code lines without
> changing the previous behaviour. Or am I missing something?

While on several places the newer code is simpler, the end goal here is
to replace all occurrences of pm_runtime_get_sync() from the media 
subsystem, due to the number of problems we're having with this:

1. despite its name, this is actually a PM runtime resume call,
   but some developers didn't seem to realize that, as I got this
   pattern on some drivers:

        pm_runtime_get_sync(&client->dev);
        pm_runtime_disable(&client->dev);
        pm_runtime_set_suspended(&client->dev);
        pm_runtime_put_noidle(&client->dev);

   It makes no sense to resume PM just to suspend it again ;-)

   The name of the new variant is a lot clearer:
	pm_runtime_resume_and_get()

2. Usual *_get() methods only increment their use count on success,
   but pm_runtime_get_sync() increments it unconditionally. Due to
   that, several drivers were mistakenly not calling
   pm_runtime_put_noidle() when it fails;

3. Consistency: we did similar changes subsystem wide with
   for instance strlcpy() and strcpy() that got replaced by
   strscpy(). Having all drivers using the same known-to-be-safe
   methods is a good thing;

4. Prevent newer drivers to copy-and-paste a code that it would
   be easier to break if they don't truly understand what's behind
   the scenes.

Thanks,
Mauro