linux-kernel - Re: [PATCH 2/3] media: platform: rzg2l-cru: rzg2l-video: Retrieve virtual channel information

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Message-ID: <CA+V-a8s4UjjDTrQ4aw3OjQuac8B-oq++KqYf-fJEQvuxD5GodA@mail.gmail.com>
Date: Sun, 8 Sep 2024 21:23:52 +0100
From: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Sakari Ailus <sakari.ailus@...ux.intel.com>, 
	Mauro Carvalho Chehab <mchehab@...nel.org>, Hans Verkuil <hverkuil-cisco@...all.nl>, 
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-renesas-soc@...r.kernel.org, Biju Das <biju.das.jz@...renesas.com>, 
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>, 
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH 2/3] media: platform: rzg2l-cru: rzg2l-video: Retrieve
 virtual channel information

Hi Laurent,

On Sat, Sep 7, 2024 at 10:09 PM Lad, Prabhakar
<prabhakar.csengg@...il.com> wrote:
>
> Hi Laurent,
>
> Thank you for the review.
>
> On Sat, Sep 7, 2024 at 12:10 AM Laurent Pinchart
> <laurent.pinchart@...asonboard.com> wrote:
<snip>
> > > +
> > >  int rzg2l_cru_start_image_processing(struct rzg2l_cru_dev *cru)
> > >  {
> > >       struct v4l2_mbus_framefmt *fmt = rzg2l_cru_ip_get_src_fmt(cru);
> > >       unsigned long flags;
> > >       int ret;
> > >
> > > +     ret = rzg2l_cru_get_virtual_channel(cru);
> > > +     if (ret < 0)
> > > +             return ret;
> > > +     cru->csi.channel = ret;
> >
> > How about passing the value to the function that needs it, instead of
> > storing it in cru->csi.channel ? You can do that on top and drop the
> > csi.channel field.
> >
> OK, let me check if this can be done.
>
The virtual channel number is programmed in rzg2l_cru_csi2_setup() [0]
call, below is the code flow of the call. This code flow is called by
spinlock held.

rzg2l_cru_start_image_processing()
    rzg2l_cru_initialize_image_conv()
        rzg2l_cru_csi2_setup()

When rzg2l_cru_get_virtual_channel() is called directly in
rzg2l_cru_csi2_setup() function we get "BUG: Invalid wait context"
(when PROVE_LOCKING is enabled) this is due to we do a mutex lock as
part of v4l2_subdev_lock_and_get_active_state() in get_frame_desc.

So probably I'll leave this as it is now.

[0] https://elixir.bootlin.com/linux/v6.10.8/source/drivers/media/platform/renesas/rzg2l-cru/rzg2l-video.c#L311

Cheers,
Prabhakar