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Date:   Fri, 28 Oct 2022 12:22:04 +0000
From:   Sakari Ailus <sakari.ailus@linux.intel.com>
To:     "Lad, Prabhakar" <prabhakar.csengg@gmail.com>
Cc:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Jacopo Mondi <jacopo@jmondi.org>,
        Niklas =?iso-8859-1?Q?S=F6derlund?= 
        <niklas.soderlund@ragnatech.se>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        linux-media@vger.kernel.org, devicetree@vger.kernel.org,
        linux-renesas-soc@vger.kernel.org, linux-kernel@vger.kernel.org,
        Biju Das <biju.das.jz@bp.renesas.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Subject: Re: [PATCH v4 4/4] media: platform: Add Renesas RZ/G2L CRU driver
Message-ID: <Y1vJbJfFjV9jRNzz@paasikivi.fi.intel.com>
References: <20221027103104.74576-1-prabhakar.mahadev-lad.rj@bp.renesas.com>
 <20221027103104.74576-5-prabhakar.mahadev-lad.rj@bp.renesas.com>
 <Y1qCbUoLrR6qlQwa@paasikivi.fi.intel.com>
 <CA+V-a8seroka4YkyCnSYa2KMPDWMG1Zk8tyiqRntdPUQnc+nrA@mail.gmail.com>
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Hi Prabhakar,

On Thu, Oct 27, 2022 at 08:04:40PM +0100, Lad, Prabhakar wrote:
...
> > > +static int rzg2l_cru_ip_s_stream(struct v4l2_subdev *sd, int enable)
> > > +{
> > > +     struct rzg2l_cru_dev *cru;
> > > +     int ret;
> > > +
> > > +     cru = v4l2_get_subdevdata(sd);
> > > +
> > > +     if (!cru->is_csi)
> > > +             return -EINVAL;
> > > +
> > > +     ret = v4l2_subdev_call(cru->ip.remote, video, s_stream, enable);
> >
> > It's up to the driver how call pre_streamon() and post_streamoff(), as long
> > as it takes place on both sides of s_stream().
> >
> > In other words, as it seems your device doesn't need anything special, you
> > could waive implemeting the callbacks yourself and call pre_streamon() and
> > post_streamoff() here.
> >
> Here the cru->ip.remote = CSI, in the rzg2l_cru_set_stream(1) where we
> are calling pre_streamon()/post_streamoff() callbacks the subdev is
> CRU-IP. So the calls from rzg2l_cru_set_stream() land into
> rzg2l_cru_ip_pre_streamon() and rzg2l_cru_ip_post_streamoff() which
> are calling pre_streamon/post_streamoff for the CSI subdev.

Again, you should call the source sub-device's pre_streamon and
post_streamoff from the s_stream handler (not from
rzg2l_cru_ip_pre_streamon or rzg2l_cru_ip_post_streamoff).

Starting streaming takes place link by link. This allows a driver to omit
implementing pre_streamon and post_streamon callbacks if it doesn't need
them.

-- 
Kind regards,

Sakari Ailus