Hi Tomasz,
On 04/06/2021 14:13, Tomasz Figa wrote:
Hi Tomi,
On Mon, Apr 12, 2021 at 02:02:09PM +0300, Tomi Valkeinen wrote:
On some platforms a video device can capture either video data or
metadata. The driver can implement vidioc functions for both video and
metadata, and use a single vb2_queue for the buffers. However, vb2_queue
requires choosing a single buffer type, which conflicts with the idea of
capturing either video or metadata.
The buffer type of vb2_queue can be changed, but it's not obvious how
this should be done in the drivers. To help this, add a new helper
function vb2_queue_change_type() which ensures the correct checks and
documents how it can be used.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
---
drivers/media/common/videobuf2/videobuf2-v4l2.c | 14 ++++++++++++++
include/media/videobuf2-v4l2.h | 15 +++++++++++++++
2 files changed, 29 insertions(+)
Good to see you contributing to the media subsystem. Not sure if you
still remember me from the Common Display Framework discussions. ;)
I barely remember CDF... ;)
Anyway, thanks for the patch. I think the code itself is okay, but I'm
wondering why the driver couldn't just have two queues, one for each
type?
There was an email thread about this:
https://www.spinics.net/lists/linux-media/msg189144.html
struct video_device has 'queue' field, so if you have two queues, you'd
need to change the vd->queue based on the format. Possibly that could be
a solution too (and, if I recall right, that's what I initially tried as
a quick hack). Changing the whole queue sounds riskier than changing
just the type.
Tomi
