Re: [RESEND PATCH v4 03/21] staging: media: tegra-video: fix .vidioc_enum_fmt_vid_cap to return all formats

From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: Luca Ceresoli <luca.ceresoli@bootlin.com>,
	Thierry Reding <thierry.reding@gmail.com>,
	Jonathan Hunter <jonathanh@nvidia.com>,
	Sowjanya Komatineni <skomatineni@nvidia.com>,
	David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
	Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Dmitry Osipenko <digetx@gmail.com>,
	linux-media@vger.kernel.org, linux-tegra@vger.kernel.org,
	dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-staging@lists.linux.dev,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Paul Kocialkowski <paul.kocialkowski@bootlin.com>,
	Richard Leitner <richard.leitner@skidata.com>
Subject: Re: [RESEND PATCH v4 03/21] staging: media: tegra-video: fix .vidioc_enum_fmt_vid_cap to return all formats
Date: Wed, 5 Apr 2023 17:30:18 +0300	[thread overview]
Message-ID: <20230405143018.GC9915@pendragon.ideasonboard.com> (raw)
In-Reply-To: <dddd76a7-f882-f1dd-0781-fcc1f9b4e060@xs4all.nl>

Hi Hans,

On Wed, Apr 05, 2023 at 10:50:37AM +0200, Hans Verkuil wrote:
> On 05/04/2023 10:31, Luca Ceresoli wrote:
> > On Wed, 5 Apr 2023 05:30:48 +0300 Laurent Pinchart wrote:
> >> On Tue, Apr 04, 2023 at 04:12:51PM +0200, Luca Ceresoli wrote:
> >>> On Wed, 29 Mar 2023 13:16:22 +0200 Hans Verkuil wrote:
> >>>   
> >>>> Hi Luca,
> >>>>
> >>>> I finally found the time to test this series. It looks OK, except for this patch.  
> >>>
> >>> Thank you very much for taking the time!
> >>>   
> >>>> The list of supported formats really has to be the intersection of what the tegra
> >>>> supports and what the sensor supports.
> >>>>
> >>>> Otherwise you would advertise pixelformats that cannot be used, and the application
> >>>> would have no way of knowing that.  
> >>>
> >>> As far as I understand, I think we should rather make this driver fully
> >>> behave as an MC-centric device. It is already using MC quite
> >>> successfully after all.
> >>>
> >>> Do you think this is correct?  
> >>
> >> Given the use cases for this driver, I agree.
> 
> I disagree.
> 
> This driver doesn't use the media controller for anything at the moment. The
> /dev/mediaX device just shows the internal topology (i.e. connected sensors),
> but otherwise it does nothing.
> 
> While it would be great if we could unlock the ISP on the Tegra, the reality
> is that it is entirely closed source and can't be used in a linux driver, and
> that's not going to change, sadly.

Never say never :-)

> That leaves us with just a basic CSI capture driver. Rather than trying to
> change this driver to a full MC device with no benefits, just drop this change
> and get your code in.

Can't the hardware support capturing different virtual channels or data
types from the same CSI-2 source ? That would require MC support, the
stream API requires subdev device nodes.

> Note that this driver will stay in staging since it still fails when I try to
> capture from two sensors at the same time: syncpoint errors start appearing
> in that case. I think there are locking issues. I think I have someone to take
> a look at that, but first I want your series to get merged.
> 
> In the very unlikely event that the ISP can be implemented in a linux driver,
> it will probably become a new driver.
> 
> Regards,
> 
> > Ok, thanks for the feedback. I will send a v5 with this change.

-- 
Regards,

Laurent Pinchart