linux-kernel - Re: [PATCH 2/3] media: i2c: imx219: Serialize during stream start/stop

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Message-ID: <CA+V-a8sSmQkXDf5CZZWKVipWWdKpE55DLLbOgktR-4VmQqmkWQ@mail.gmail.com>
Date:   Wed, 10 Mar 2021 13:08:20 +0000
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Pavel Machek <pavel@...x.de>,
        Andrey Konovalov <andrey.konovalov@...aro.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Jacopo Mondi <jacopo@...ndi.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        linux-media <linux-media@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Biju Das <biju.das.jz@...renesas.com>
Subject: Re: [PATCH 2/3] media: i2c: imx219: Serialize during stream start/stop

Hi Laurent,

On Wed, Mar 10, 2021 at 12:54 PM Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> Hi Prabhakar,
>
> On Wed, Mar 10, 2021 at 12:46:39PM +0000, Lad, Prabhakar wrote:
> > On Wed, Mar 10, 2021 at 12:40 PM Laurent Pinchart wrote:
> > > On Wed, Mar 10, 2021 at 12:20:13PM +0000, Lad Prabhakar wrote:
> > > > Serialize during stream start/stop in suspend/resume callbacks.
> > >
> > > Could you please explain why this is needed ?
> > >
> > The streaming variable in this driver has serialized access, but this
> > wasn't taken care during suspend/resume callbacks.
>
> But nothing that touches the streaming variable can run concurrently to
> suspend/resume, isn't it ?
>
You are right, we could drop this patch.

> I'm actually even quite dubious about the need to start and stop
> streaming during resume and suspend, the driver using the subdev should
> start/stop the whole video pipeline at suspend/resume time.
>
I see, do we have any documentation on how bridge/subdevs should
behave on suspend/resume ?

I did have a quick look at the omp3isp bridge driver and it does
start/stop on resume/suspend callbacks.

Cheers,
Prabhakar

> > > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > > > ---
> > > >  drivers/media/i2c/imx219.c | 5 +++++
> > > >  1 file changed, 5 insertions(+)
> > > >
> > > > diff --git a/drivers/media/i2c/imx219.c b/drivers/media/i2c/imx219.c
> > > > index f0cf1985a4dc..87c021de1460 100644
> > > > --- a/drivers/media/i2c/imx219.c
> > > > +++ b/drivers/media/i2c/imx219.c
> > > > @@ -1172,8 +1172,10 @@ static int __maybe_unused imx219_suspend(struct device *dev)
> > > >       struct v4l2_subdev *sd = dev_get_drvdata(dev);
> > > >       struct imx219 *imx219 = to_imx219(sd);
> > > >
> > > > +     mutex_lock(&imx219->mutex);
> > > >       if (imx219->streaming)
> > > >               imx219_stop_streaming(imx219);
> > > > +     mutex_unlock(&imx219->mutex);
> > > >
> > > >       return 0;
> > > >  }
> > > > @@ -1184,11 +1186,13 @@ static int __maybe_unused imx219_resume(struct device *dev)
> > > >       struct imx219 *imx219 = to_imx219(sd);
> > > >       int ret;
> > > >
> > > > +     mutex_lock(&imx219->mutex);
> > > >       if (imx219->streaming) {
> > > >               ret = imx219_start_streaming(imx219);
> > > >               if (ret)
> > > >                       goto error;
> > > >       }
> > > > +     mutex_unlock(&imx219->mutex);
> > > >
> > > >       return 0;
> > > >
> > > > @@ -1197,6 +1201,7 @@ static int __maybe_unused imx219_resume(struct device *dev)
> > > >       imx219->streaming = false;
> > > >       __v4l2_ctrl_grab(imx219->vflip, false);
> > > >       __v4l2_ctrl_grab(imx219->hflip, false);
> > > > +     mutex_unlock(&imx219->mutex);
> > > >
> > > >       return ret;
> > > >  }
>
> --
> Regards,
>
> Laurent Pinchart