linux-kernel - Re: [PATCH v4 4/4] media: platform: Add Renesas RZ/G2L CRU driver

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Date:   Sun, 30 Oct 2022 22:32:43 +0000
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Jacopo Mondi <jacopo@...ndi.org>,
        Niklas Söderlund <niklas.soderlund@...natech.se>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Biju Das <biju.das.jz@...renesas.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v4 4/4] media: platform: Add Renesas RZ/G2L CRU driver

Hi Sakari,

On Fri, Oct 28, 2022 at 1:22 PM Sakari Ailus
<sakari.ailus@...ux.intel.com> wrote:
>
> 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.
>
Thank you for the explanation that makes sense now to me.

Now with this approach the initialization sequence of CSI + CRU won't
align as per the HW manual. Unfortunately I'll have to switch back on
exporting the functions. I hope that's okay?

Cheers,
Prabhakar