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Date:   Mon, 2 Oct 2023 16:51:28 -0700
From:   Deborah Brouwer <deborah.brouwer@collabora.com>
To:     Hans Verkuil <hverkuil@xs4all.nl>
Cc:     Nicolas Dufresne <nicolas.dufresne@collabora.com>,
        Sebastian Fricke <sebastian.fricke@collabora.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Nas Chung <nas.chung@chipsnmedia.com>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Fabio Estevam <festevam@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Shawn Guo <shawnguo@kernel.org>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Jackson Lee <jackson.lee@chipsnmedia.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        NXP Linux Team <linux-imx@nxp.com>,
        Conor Dooley <conor+dt@kernel.org>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        Benjamin Gaignard <benjamin.gaignard@collabora.com>,
        devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        Robert Beckett <bob.beckett@collabora.com>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel@collabora.com
Subject: Re: [PATCH v12 5/7] media: chips-media: wave5: Add the v4l2 layer
Message-ID: <ZRtXgMhSS3D6H3/4@db550>
References: <20230915-wave5_v12_on_media_master-v12-0-92fc66cd685d@collabora.com>
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On Wed, Sep 27, 2023 at 09:19:46AM +0200, Hans Verkuil wrote:
> On 27/09/2023 01:29, Nicolas Dufresne wrote:
> > Le vendredi 22 septembre 2023 ? 09:33 +0200, Hans Verkuil a ?crit?:
> >> On 21/09/2023 21:11, Nicolas Dufresne wrote:
> >>> Le mercredi 20 septembre 2023 ? 17:13 +0200, Hans Verkuil a ?crit?:
> >>>> On 15/09/2023 23:11, Sebastian Fricke wrote:
> >>>>> From: Nas Chung <nas.chung@chipsnmedia.com>
> >>>>>
> >>>>> Add the decoder and encoder implementing the v4l2
> >>>>> API. This patch also adds the Makefile and the VIDEO_WAVE_VPU config
> >>>>>
> >>>>> Signed-off-by: Sebastian Fricke <sebastian.fricke@collabora.com>
> >>>>> Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
> >>>>> Signed-off-by: Robert Beckett <bob.beckett@collabora.com>
> >>>>> Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
> >>>>> Signed-off-by: Nas Chung <nas.chung@chipsnmedia.com>
> >>>>> ---
> >>>>>  drivers/media/platform/chips-media/Kconfig         |    1 +
> >>>>>  drivers/media/platform/chips-media/Makefile        |    1 +
> >>>>>  drivers/media/platform/chips-media/wave5/Kconfig   |   12 +
> >>>>>  drivers/media/platform/chips-media/wave5/Makefile  |   10 +
> >>>>>  .../platform/chips-media/wave5/wave5-helper.c      |  196 ++
> >>>>>  .../platform/chips-media/wave5/wave5-helper.h      |   30 +
> >>>>>  .../platform/chips-media/wave5/wave5-vpu-dec.c     | 1965 ++++++++++++++++++++
> >>>>>  .../platform/chips-media/wave5/wave5-vpu-enc.c     | 1825 ++++++++++++++++++
> >>>>>  .../media/platform/chips-media/wave5/wave5-vpu.c   |  331 ++++
> >>>>>  .../media/platform/chips-media/wave5/wave5-vpu.h   |   83 +
> >>>>>  10 files changed, 4454 insertions(+)
> >>>>>
> >>
> >> <snip>
> >>
> >>>>> +static int wave5_vpu_dec_set_eos_on_firmware(struct vpu_instance *inst)
> >>>>> +{
> >>>>> +	int ret;
> >>>>> +
> >>>>> +	ret = wave5_vpu_dec_update_bitstream_buffer(inst, 0);
> >>>>> +	if (ret) {
> >>>>> +		dev_err(inst->dev->dev,
> >>>>> +			"Setting EOS for the bitstream, fail: %d\n", ret);
> >>>>
> >>>> Is this an error due to a driver problem, or because a bad bitstream is
> >>>> fed from userspace? In the first case, dev_err would be right, in the
> >>>> second dev_dbg would be more appropriate. Bad userspace input should not
> >>>> spam the kernel log in general.
> >>>
> >>> Its the first. To set the EOS flag, a command is sent to the firmware. That
> >>> command may never return (timeout) or may report an error. For this specific
> >>> command, if that happens we are likely facing firmware of driver problem (or
> >>> both).
> >>
> >> OK, I'd add that as a comment here as this is unexpected behavior.
> >>
> >>>
> >>>>
> >>>>> +		return ret;
> >>>>> +	}
> >>>>> +	return 0;
> >>>>> +}
> >>
> >> <snip>
> >>
> >>>>> +static int wave5_vpu_dec_create_bufs(struct file *file, void *priv,
> >>>>> +				     struct v4l2_create_buffers *create)
> >>>>> +{
> >>>>> +	struct v4l2_format *f = &create->format;
> >>>>> +
> >>>>> +	if (f->type == V4L2_BUF_TYPE_VIDEO_CAPTURE)
> >>>>> +		return -ENOTTY;
> >>>>
> >>>> Huh? Why is this needed?
> >>>
> >>> Minimally a comment should be added. The why is that we support CREATE_BUF for
> >>> OUTPUT queue (bitstream) but not for CAPTURE queues. This is simply not
> >>> supported by Wave5 firmware. Do you have any suggestion how this asymmetry can
> >>> be implemented better ?
> >>
> >> Certainly not with ENOTTY: the ioctl exists, it is just not supported for
> >> CAPTURE queues.
> >>
> >> How about -EPERM? And document this error as well in the VIDIOC_CREATE_BUFS
> >> documentation. And you want a dev_dbg here too.
> > 
> > The suggestion cannot be used since there is documentation for that one already,
> > and it does not match "unsupported".
> > 
> > "Permission denied. Can be returned if the device needs write permission, or
> > some special capabilities is needed (e. g. root)"
> > 
> > What about using the most logical error code, which name is actually obvious,
> > like ENOTSUP ?
> > 
> >    #define ENOTSUPP	524	/* Operation is not supported */
> > 
> 
> Let's go with EOPNOTSUPP. That seems to be the more commonly used error
> code in drivers.

Hi Hans,

Sorry to belabour this issue but when I change the return value
to EOPNOTSUPP, it now causes v4l2-compliance to fail because
v4l2-test-buffers.cpp expects ENOTTY if CREATE_BUFS is not supported.

We didn't get this warning before because there was a typo in the
buffer check and it was only checking for single-planar buffers.

How would you prefer to handle this? The options seem like
keep ENOTTY in this driver or
patch v4l2-compliance to warn if it also receives EOPNOTSUPP?

> 
> >>
> >> So I would propose that EPERM is returned if CREATE_BUFS is only supported
> >> for for one of the two queues of an M2M device.
> > 
> > Note that userspace does not care of the difference between an ioctl not being
> > implemented at all or not being implement for one queue. GStreamer have been
> > testing with both queue type for couple of years now. Adding this distinction is
> > just leaking an implementation details to userspace. I'm fine to just do what
> > you'd like, just stating the obvious that while it may look logical inside the
> > kernel, its a bit of a non-sense for our users.
> 
> I don't agree with that. If an ioctl returns ENOTTY, then userspace can be certain
> that that ioctl is not implemented for the given file descriptor. That's not the case
> here: it is implemented, the operation is just not supported for one of the queues.
> 
> Regards,
> 
> 	Hans