linux-kernel - Re: [PATCH v4 5/8] media: v4l2-core: Introduce v4l2-params.c

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Message-ID: <20250915144040.GA8821@pendragon.ideasonboard.com>
Date: Mon, 15 Sep 2025 17:40:40 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Jacopo Mondi <jacopo.mondi@...asonboard.com>
Cc: kernel test robot <lkp@...el.com>,
	Dafna Hirschfeld <dafna@...tmail.com>,
	Keke Li <keke.li@...ogic.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Heiko Stuebner <heiko@...ech.de>,
	Dan Scally <dan.scally@...asonboard.com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	oe-kbuild-all@...ts.linux.dev, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-rockchip@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 5/8] media: v4l2-core: Introduce v4l2-params.c

On Mon, Sep 15, 2025 at 03:31:58PM +0200, Jacopo Mondi wrote:
> Question for media maintainers...
> 
> I'm not sure how I should better handle this one
> 
> On Sun, Aug 24, 2025 at 07:16:21AM +0800, kernel test robot wrote:
> > Hi Jacopo,
> >
> > kernel test robot noticed the following build errors:
> >
> > [auto build test ERROR on a75b8d198c55e9eb5feb6f6e155496305caba2dc]
> >
> > url:    https://github.com/intel-lab-lkp/linux/commits/Jacopo-Mondi/media-uapi-Introduce-V4L2-extensible-params/20250820-210503
> > base:   a75b8d198c55e9eb5feb6f6e155496305caba2dc
> > patch link:    https://lore.kernel.org/r/20250820-extensible-parameters-validation-v4-5-30fe5a99cb1f%40ideasonboard.com
> > patch subject: [PATCH v4 5/8] media: v4l2-core: Introduce v4l2-params.c
> > config: nios2-randconfig-002-20250824 (https://download.01.org/0day-ci/archive/20250824/202508240704.AZwGXBaw-lkp@intel.com/config)
> > compiler: nios2-linux-gcc (GCC) 9.5.0
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250824/202508240704.AZwGXBaw-lkp@intel.com/reproduce)
> >
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@...el.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202508240704.AZwGXBaw-lkp@intel.com/
> >
> > All errors (new ones prefixed by >>):
> >
> >    nios2-linux-ld: drivers/media/v4l2-core/v4l2-params.o: in function `v4l2_params_buffer_validate':
> >    v4l2-params.c:(.text+0x124): undefined reference to `vb2_plane_vaddr'
> > >> v4l2-params.c:(.text+0x124): relocation truncated to fit: R_NIOS2_CALL26 against `vb2_plane_vaddr'
> 
> Clearly v4l2-params.c (now v4l2-isp.c) depends on VIDEOBUF2_CORE
> 
> Right now v4l2-params.c gets compiled in as part of the
> videodev-objs Makefile target. IOW is not gated by a KConfig option.
> 
> To select (or better, depend) on VIDEOBUF2_CORE I should guard
> v4l2-params.c with a KConfig option so that I can 'depend on
> VIDEOBUF2_CORE'. Drivers that use the v4l2-params.c helper would then
> have to 'select V4L2_PARAMS` (or similar).

Make it V4L2_ISP :-)

> Is this the best approach or are there alternatives I might be missing ?

We don't want VIDEODEV depending on VB2. I think it also makes sense to
have a separate Kconfig option for these helpers, are they will be used
by a small number of drivers.

Make CONFIG_V4L2_ISP an option that drivers select, not depend on.

-- 
Regards,

Laurent Pinchart