linux-kernel - Re: [PATCH 38/78] media: i2c: mt9m001: use pm_runtime_resume_and

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Message-ID: <YIlNY7xJYmqtxVOe@hovoldconsulting.com>
Date:   Wed, 28 Apr 2021 13:56:19 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Cc:     Jacopo Mondi <jacopo@...ndi.org>, linuxarm@...wei.com,
        mauro.chehab@...wei.com, Hans Verkuil <hverkuil-cisco@...all.nl>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org
Subject: Re: [PATCH 38/78] media: i2c: mt9m001: use
 pm_runtime_resume_and_get()

On Wed, Apr 28, 2021 at 01:28:53PM +0200, Mauro Carvalho Chehab wrote:
> Em Wed, 28 Apr 2021 12:05:26 +0200
> Johan Hovold <johan@...nel.org> escreveu:

> > Right, a resume failure is a pretty big issue and it's not really clear
> > how to to even handle that generally. But at remove() time you don't
> > have much choice but to go on and release resource anyway. 
> > 
> > So unless actually implementing some error handling too, using
> > pm_runtime_sync_get() without checking for errors is still preferred
> > over pm_runtime_resume_and_get(). That is 
> > 
> > 	pm_runtime_get_sync();
> > 	/* cleanup */
> > 	pm_runtime_disable()
> > 	pm_runtime_put_noidle();
> > 
> > is better than:
> > 
> > 	ret = pm_runtime_resume_and_get();
> > 	/* cleanup */
> > 	pm_runtime_disable();
> > 	if (ret == 0)
> > 		pm_runtime_put_noidle();
> > 
> > unless you also start doing something ret.
> 
> Perhaps the best would be to use, instead:
> 
> 	pm_runtime_get_noresume();
>  	/* cleanup */
>  	pm_runtime_disable()
>  	pm_runtime_put_noidle();
> 	pm_runtime_set_suspended();
> 
> I mean, at least for my eyes, it doesn't make sense to do a PM
> resume during driver's removal/unbind time.

The cleanup bit above would depend on the device being resumed so using
pm_runtime_get_noresume() makes little sense.

Some drivers disable clocks etc explicitly at remove instead of relying
on pm runtime for that and then they'd use the above scheme (plus
explicit pm_runtime_set_suspended()).

Johan