linux-kernel - Re: [PATCH v12 5/7] media: chips-media: wave5: Add the v4l2 layer

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Message-ID: <e9a6c88d-d7f0-41a0-b8c6-e10f01bffdfa@xs4all.nl>
Date:   Tue, 3 Oct 2023 08:54:28 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Deborah Brouwer <deborah.brouwer@...labora.com>
Cc:     Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        Sebastian Fricke <sebastian.fricke@...labora.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Nas Chung <nas.chung@...psnmedia.com>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Jackson Lee <jackson.lee@...psnmedia.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        NXP Linux Team <linux-imx@....com>,
        Conor Dooley <conor+dt@...nel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Benjamin Gaignard <benjamin.gaignard@...labora.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Robert Beckett <bob.beckett@...labora.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com
Subject: Re: [PATCH v12 5/7] media: chips-media: wave5: Add the v4l2 layer

Hi Deb,

On 03/10/2023 01:51, Deborah Brouwer wrote:
> 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 à 09:33 +0200, Hans Verkuil a écrit :
>>>> On 21/09/2023 21:11, Nicolas Dufresne wrote:
>>>>> Le mercredi 20 septembre 2023 à 17:13 +0200, Hans Verkuil a écrit :
>>>>>> On 15/09/2023 23:11, Sebastian Fricke wrote:
>>>>>>> From: Nas Chung <nas.chung@...psnmedia.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@...labora.com>
>>>>>>> Signed-off-by: Nicolas Dufresne <nicolas.dufresne@...labora.com>
>>>>>>> Signed-off-by: Robert Beckett <bob.beckett@...labora.com>
>>>>>>> Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@...labora.com>
>>>>>>> Signed-off-by: Nas Chung <nas.chung@...psnmedia.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?

You patch v4l2-compliance. It makes sense: we're making a uAPI modification,
so that implies changes to v4l2-compliance.

So v4l2-compliance needs to understand EOPNOTSUPP for CREATE_BUFS: if it is
returned it has to check that it is used correctly: so there has to be at
least one buffer type for which CREATE_BUFS actually works. In other words,
v4l2-compliance must check that EOPNOTSUPP isn't used as a replacement
for ENOTTY.

This can be done in testReqBufs().

Regards,

	Hans