On Fri, Jun 4, 2021 at 11:09 PM Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx> wrote: > > 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. Okay, I see. Thanks for the pointer. Generally I'm fine with this, although it's worth noting that it's not true that one video_device can only have 1 queue. See the numerous mem-to-mem devices, which use two queues simultaneously. Anyway, Acked-by: Tomasz Figa <tfiga@xxxxxxxxxxxx> Best regards, Tomasz
