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

[Hans Verkuil]

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@xxxxxxxxxxxxxxx>
>>>>>
>>>>> 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@xxxxxxxxxxxxx>
>>>>> Signed-off-by: Nicolas Dufresne <nicolas.dufresne@xxxxxxxxxxxxx>
>>>>> Signed-off-by: Robert Beckett <bob.beckett@xxxxxxxxxxxxx>
>>>>> Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@xxxxxxxxxxxxx>
>>>>> Signed-off-by: Nas Chung <nas.chung@xxxxxxxxxxxxxxx>
>>>>> ---
>>>>>  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.

>>
>> 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