Re: [PATCH v3] Add tw5864 driver

[Andrey Utkin <andrey_utkin@fastmail.com>]

Thanks for review Hans!

On Mon, Jul 11, 2016 at 07:58:38AM +0200, Hans Verkuil wrote:
> > +" v4l2-ctl --device $dev --set-ctrl=video_gop_size=1; done\n"
> 
> Replace $dev by /dev/videoX
> 
> Wouldn't it make more sense to default to this? And show the warning only if
> P-frames are enabled?

I believe it's better to leave P-frames on by default. All-I-frames
stream has huge bitrate. And the pixels artifacts is not very strong,
it's 0 - 10 bad pixels on picture at same time in our dev environment,
and probably up to 50 bad pixels max in other environments I know of.

> > +	dma_sync_single_for_cpu(&dev->pci->dev, cur_frame->vlc.dma_addr,
> > +				H264_VLC_BUF_SIZE, DMA_FROM_DEVICE);
> > +	dma_sync_single_for_cpu(&dev->pci->dev, cur_frame->mv.dma_addr,
> > +				H264_MV_BUF_SIZE, DMA_FROM_DEVICE);
> 
> This is almost certainly the wrong place. This should probably happen in the
> tasklet. The tasklet runs after the isr, so by the time the tasklet runs
> you've already called dma_sync_single_for_device.

Thanks, moved to tasklet subroutine tw5864_handle_frame().

I didn't seem to me like dma_sync_single_for_* can take long time or be
otherwise bad to be done from interrupt context.

> > +static int tw5864_querycap(struct file *file, void *priv,
> > +			   struct v4l2_capability *cap)
> > +{
> > +	struct tw5864_input *input = video_drvdata(file);
> > +
> > +	strcpy(cap->driver, "tw5864");
> > +	snprintf(cap->card, sizeof(cap->card), "TW5864 Encoder %d",
> > +		 input->nr);
> > +	sprintf(cap->bus_info, "PCI:%s", pci_name(input->root->pci));
> > +	cap->device_caps = V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_READWRITE |
> > +		V4L2_CAP_STREAMING;
> > +	cap->capabilities = cap->device_caps | V4L2_CAP_DEVICE_CAPS;
> 
> This line can be dropped, the core will fill in the capabilities field for you.

No, removing this line causes v4l2-compliance failures and also ffmpeg fails to
play the device.

Required ioctls:
                fail: v4l2-compliance.cpp(550): dcaps & ~caps
        test VIDIOC_QUERYCAP: FAIL

Allow for multiple opens:
        test second video open: OK
                fail: v4l2-compliance.cpp(550): dcaps & ~caps
        test VIDIOC_QUERYCAP: FAIL