Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20221014183459.181567-1-prabhakar.mahadev-lad.rj@bp.renesas.com>
 <20221014183459.181567-3-prabhakar.mahadev-lad.rj@bp.renesas.com>
 <Y1pphVPw0J97AmW4@paasikivi.fi.intel.com> <CA+V-a8szaPjwumrBgOT9gzMKBjY7hk0zfP8RgzUUDfY+BAsogA@mail.gmail.com>
 <Y1p91+XxPCB9NWwh@paasikivi.fi.intel.com> <CA+V-a8uhYymEVg7jdLVGNLsVD3=O1mk-_NVERu00W+gsv-7QXg@mail.gmail.com>
 <Y1rQBmXj71C1RrwB@paasikivi.fi.intel.com> <Y1/a4QUQpykhuXwh@paasikivi.fi.intel.com>
In-Reply-To: <Y1/a4QUQpykhuXwh@paasikivi.fi.intel.com>
From:   "Lad, Prabhakar" <prabhakar.csengg@gmail.com>
Date:   Mon, 31 Oct 2022 16:10:45 +0000
Message-ID: <CA+V-a8vQkvO5k=b169SfiD5qdn9hNOJk6y2GHns1OkrnxHXeXQ@mail.gmail.com>
Subject: Re: [PATCH v2 2/5] media: i2c: ov5645: Use runtime PM
To:     Sakari Ailus <sakari.ailus@linux.intel.com>
Cc:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Hans Verkuil <hverkuil@xs4all.nl>,
        Shawn Tu <shawnx.tu@intel.com>,
        Jacopo Mondi <jacopo@jmondi.org>, linux-media@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-renesas-soc@vger.kernel.org,
        Biju Das <biju.das.jz@bp.renesas.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Hi Sakari,

On Mon, Oct 31, 2022 at 2:25 PM Sakari Ailus
<sakari.ailus@linux.intel.com> wrote:
>
> Hi Prabhakar,
>
> On Thu, Oct 27, 2022 at 06:37:58PM +0000, Sakari Ailus wrote:
> > 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@linux.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@linux.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.
>
> There are various ways how runtime PM interface functions generally work,
> and generally return an error when runtime PM is disabled. Incrementing the
> usage_count when runtime PM is disabled would make
> pm_runtime_get_if_in_use() very special and not match what the rest would
> do. Therefore I think it's best to keep this in the driver. After all, mo
> other driver needs this in the media tree, which is the major user of the
> function.
>
Thank you for digging deep into this. I'll keep it as is and send a v3.

Cheers,
Prabhakar