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

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Message-ID: <CA+V-a8uhYymEVg7jdLVGNLsVD3=O1mk-_NVERu00W+gsv-7QXg@mail.gmail.com>
Date:   Thu, 27 Oct 2022 17:32:07 +0100
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.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 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);

    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);


Cheers,
Prabhakar