linux-kernel - Re: [PATCH v2 2/5] media: i2c: ov5645: Use runtime PM

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Message-ID: <Y1rQBmXj71C1RrwB@paasikivi.fi.intel.com>
Date:   Thu, 27 Oct 2022 18:37:58 +0000
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil@...all.nl>,
        Shawn Tu <shawnx.tu@...el.com>,
        Jacopo Mondi <jacopo@...ndi.org>, linux-media@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org,
        Biju Das <biju.das.jz@...renesas.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v2 2/5] media: i2c: ov5645: Use runtime PM

Hi Prabhakar,

On Thu, Oct 27, 2022 at 05:32:07PM +0100, Lad, Prabhakar wrote:
> Hi Sakari,
> 
> On Thu, Oct 27, 2022 at 1:47 PM Sakari Ailus
> <sakari.ailus@...ux.intel.com> wrote:
> >
> > Hi Prabhakar,
> >
> > On Thu, Oct 27, 2022 at 01:01:52PM +0100, Lad, Prabhakar wrote:
> > > Hi Sakari,
> > >
> > > On Thu, Oct 27, 2022 at 12:20 PM Sakari Ailus
> > > <sakari.ailus@...ux.intel.com> wrote:
> > > >
> > > > Hi Prabhakar,
> > > >
> > > > One more comment.
> > > >
> > > > On Fri, Oct 14, 2022 at 07:34:56PM +0100, Prabhakar wrote:
> > > > > @@ -1209,12 +1190,16 @@ static int ov5645_probe(struct i2c_client *client)
> > > > >
> > > > >       dev_info(dev, "OV5645 detected at address 0x%02x\n", client->addr);
> > > > >
> > > > > +     pm_runtime_set_active(dev);
> > > > > +     pm_runtime_get_noresume(dev);
> > > > > +     pm_runtime_enable(dev);
> > > >
> > > > You won't gain anything by eanbling runtime PM here. Just move it to the
> > > > end of the function before the rest of the calls. Error handling becomes
> > > > more simple.
> > > >
> > > If I move the above calls below I get the below warning:
> > >
> > > [    2.633386] ov5645 0-003c: Runtime PM usage count underflow!
> > >
> > > This is because of the last patch which moves ov5645_entity_init_cfg()
> > > before registering the subdev. ov5645_entity_init_cfg() calls s_ctrl
> > > due to which we are seeing the above message. Please let me know how
> > > to proceed on this.
> >
> > Ah. Yes, this is a problem with the usage pattern of
> > pm_runtime_get_if_in_use(). But please don't change that.
> >
> > You can still move enabling runtime PM later in the function.
> >
> Agreed, the final version looks like below:
> 
>     pm_runtime_set_active(dev);
>     pm_runtime_get_noresume(dev);
> 

You'll have to enable runtime PM here, before pm_runtime_get_if_in_use()
gets called.

I'll see if it could be made to work in a sensible way when runtime PM
isn't enabled yet.

>     ov5645_entity_init_cfg(&ov5645->sd, NULL);
> 
>     ret = v4l2_async_register_subdev(&ov5645->sd);
>     if (ret < 0) {
>         dev_err(dev, "could not register v4l2 device\n");
>         goto err_pm_runtime;
>     }
> 
>     pm_runtime_set_autosuspend_delay(dev, 1000);
>     pm_runtime_use_autosuspend(dev);
>     pm_runtime_enable(dev);

-- 
Kind regards,

Sakari Ailus