linux-kernel - Re: [PATCH RFC v2 2/2] media: platform: pxa

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Date:	Sun, 31 Jul 2016 17:03:17 +0200
From:	Robert Jarzmik <robert.jarzmik@...e.fr>
To:	Hans Verkuil <hverkuil@...all.nl>
Cc:	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v2 2/2] media: platform: pxa_camera: make a standalone v4l2 device

Hi Hans,


Hans Verkuil <hverkuil@...all.nl> writes:
> On 04/02/2016 04:26 PM, Robert Jarzmik wrote:
>> diff --git a/drivers/media/platform/soc_camera/pxa_camera.c b/drivers/media/platform/soc_camera/pxa_camera.c
>> index b8dd878e98d6..30d266bbab55 100644
>> --- a/drivers/media/platform/soc_camera/pxa_camera.c
>> +++ b/drivers/media/platform/soc_camera/pxa_camera.c
>
> When you prepare the final patch series, please put the driver in
> drivers/media/platform/pxa-camera and not in the soc-camera directory.
Sure.
Would you accept the final patch to make the move, so that I keep the
bisectability, ie. that all patches are applied while still in ../soc_camera,
and then the final one making just the move to .../platform ?

>> +	if (format->name)
>> +		strlcpy(f->description, format->name, sizeof(f->description));
>
> You can drop this since the core fills in the description. That means the
> 'name' field of struct soc_mbus_pixelfmt is not needed either.
Ok, let's try this, for v3.

>> +static int pxac_vidioc_querycap(struct file *file, void *priv,
>> +				struct v4l2_capability *cap)
>> +{
>> +	strlcpy(cap->bus_info, "platform:pxa-camera", sizeof(cap->bus_info));
>> +	strlcpy(cap->driver, PXA_CAM_DRV_NAME, sizeof(cap->driver));
>> +	strlcpy(cap->card, pxa_cam_driver_description, sizeof(cap->card));
>> +	cap->device_caps = V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_STREAMING;
>> +	cap->capabilities = cap->device_caps | V4L2_CAP_DEVICE_CAPS;
>
> Tiny fix: you can drop the capabilities assignment: the v4l2 core does that
> for you these days.
Well, above kernel v4.7, if I drop the assignement, v4l2-compliance -s finds 2
new errors:
	Required ioctls:
			fail: v4l2-compliance.cpp(534): dcaps & ~caps
		test VIDIOC_QUERYCAP: FAIL
	
	Allow for multiple opens:
		test second video open: OK
			fail: v4l2-compliance.cpp(534): dcaps & ~caps
		test VIDIOC_QUERYCAP: FAIL
		test VIDIOC_G/S_PRIORITY: OK

So there is something fishy here if the core provides this data ...

>> +static int pxac_vidioc_enum_input(struct file *file, void *priv,
>> +				  struct v4l2_input *i)
>> +{
>> +	if (i->index > 0)
>> +		return -EINVAL;
>> +
>> +	memset(i, 0, sizeof(*i));
>
> The memset can be dropped, it's cleared for you.
OK, for v3.

>> +static void pxac_vb2_queue(struct vb2_buffer *vb)
>> +{
>> +	struct pxa_buffer *buf = vb2_to_pxa_buffer(vb);
>> +	struct pxa_camera_dev *pcdev = vb2_get_drv_priv(vb->vb2_queue);
>> +
>> +	dev_dbg(pcdev_to_dev(pcdev),
>> +		 "%s(vb=%p) nb_channels=%d size=%lu active=%p\n",
>> +		__func__, vb, pcdev->channels, vb2_get_plane_payload(vb, 0),
>> +		pcdev->active);
>> +
>> +	list_add_tail(&buf->queue, &pcdev->capture);
>> +
>> +	pxa_dma_add_tail_buf(pcdev, buf);
>> +
>> +	if (!pcdev->active)
>> +		pxa_camera_start_capture(pcdev);
>
> This is normally done from start_streaming. Are you really sure this is the right
> place? I strongly recommend moving this start_capture call.
Well, it was at least with the previous framework.
Previously this was done here to "hot-queue" a buffer :
 - if a previous capture was still running, the buffer was queued by
   pxa_dma_add_tail_buf(), and no restart of the DMA pump was necessary
 - if the previous capture was finished, a new one was initiated

Now if the new framework takes care of that, I can move the
pxa_camera_start_capture() into start_streaming(), no problem, let me try in the
next patchset. That might take a bit of time because testing both the
"hot-queue" and the "queue but hot-queuing missed" is a bit tricky.

> You may also want to use the struct vb2queue min_buffers_needed field to specify
> the minimum number of buffers that should be queued up before start_streaming can
> be called. Whether that's needed depends on your DMA engine.
I have no minimum required by the pxa dmaengine driver, that's good.

>> +
>> +	v4l2_disable_ioctl(vdev, VIDIOC_G_STD);
>> +	v4l2_disable_ioctl(vdev, VIDIOC_S_STD);
>> +	v4l2_disable_ioctl(vdev, VIDIOC_ENUMSTD);
>
> I don't think this is needed since the tvnorms field of struct video_device == 0,
> signalling that there is no STD support.
OK, for v3.

Cheers.

-- 
Robert