linux-kernel - Re: [PATCH v2 37/66] media: sun6i-csi: Move power management to runtime pm in capture

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Date:   Tue, 15 Feb 2022 23:21:03 +0200
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-phy@...ts.infradead.org,
        linux-clk@...r.kernel.org, linux-staging@...ts.linux.dev,
        Yong Deng <yong.deng@...ewell.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Maxime Ripard <mripard@...nel.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Helen Koike <helen.koike@...labora.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v2 37/66] media: sun6i-csi: Move power management to
 runtime pm in capture

Hi Paul,

On Tue, Feb 15, 2022 at 11:21:17AM +0100, Paul Kocialkowski wrote:
> Hi Laurent,
> 
> On Tue 15 Feb 22, 12:04, Laurent Pinchart wrote:
> > Hi Paul,
> > 
> > On Tue, Feb 15, 2022 at 10:56:22AM +0100, Paul Kocialkowski wrote:
> > > On Mon 14 Feb 22, 20:30, Sakari Ailus wrote:
> > > > On Sat, Feb 05, 2022 at 07:54:00PM +0100, Paul Kocialkowski wrote:
> > > > > Let's just enable the module when we start using it (at stream on)
> > > > > and benefit from runtime pm instead of enabling it at first open.
> > > > > 
> > > > > Also reorder the call to v4l2_pipeline_pm_get.
> > > > > 
> > > > > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> > > > 
> > > > Nice patch!
> > > 
> > > Thanks!
> > > 
> > > > Do you still need v4l2_pipeline_pm_put()? Removing it would be a separate
> > > > patch of course.
> > > 
> > > My understanding is that this is still useful if there are drivers in the
> > > pipeline that rely on s_power instead of rpm (a typical case could be an
> > > old sensor driver). So that's why this is kept around, but all other components
> > > of the pipeline (isp/csi/mipi csi-2) are using rpm now.
> > 
> > If that's not the case on your test platforms, I think it would be
> > better to drop support for this old API, and convert drivers that still
> > use .s_power() if someone needs to use one on an Allwinner platform.
> 
> I agree this is the path to follow but it feels like we're not quite there
> yet and a bunch of driver were not converted at this point, including some
> popular ones like ov5640, which I know for sure is used with Allwinner devices.
> 
> Honestly I'd be happy to get rid of these legacy functions as soon as the
> transition is done, but doing it now would mean breaking a significant number
> of use cases (which I'm trying to avoid here despite all the changes).
> 
> I definitely wouldn't be confident making that transition here and it
> probably wouldn't be a good idea to make that a requirement to merge this
> (already quite big) series.
> 
> What do you think?

Feel free to keep it if you prefer that.

All sensor drivers that implement s_power are old but there are quite a few
of them. Converting them isn't trivial so best done by someone who has
access to the hardware.

-- 
Regards,

Sakari Ailus