| Message ID | 86ad4808718ff07ab8ac64b62170b789c16b2581.1701349092.git.hverkuil-cisco@xs4all.nl |
|---|---|
| State | Accepted |
| Commit | 350ab13e1382f2afcc2285041a1e75b80d771c2c |
| Headers | show |
| Series | [1/3] media: bttv: start_streaming should return a proper error code | expand |
* Hans Verkuil (hverkuil-cisco@xs4all.nl) wrote: > The vb2 read support requests 1 buffer, leaving it to the driver > to increase this number to something that works. > > Unfortunately, drivers do not deal with this reliably, and in fact > this caused problems for the bttv driver and reading from /dev/vbiX, > causing every other VBI frame to be all 0. > > Instead, request as the number of buffers whatever is the maximum of > 2 and q->min_buffers_needed+1. > > In order to start streaming you need at least q->min_buffers_needed > queued buffers, so add 1 buffer for processing. And if that field > is 0, then choose 2 (again, one buffer is being filled while the > other one is being processed). > > This certainly makes more sense than requesting just 1 buffer, and > the VBI bttv support is now working again. > > It turns out that the old videobuf1 behavior of bttv was to allocate > 8 (video) and 4 (vbi) buffers when used with read(). After the vb2 > conversion that changed to 2 for both. With this patch it is 3, which > is really all you need. > > Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl> > Fixes: b7ec3212a73a ("media: bttv: convert to vb2") This looks like it's working nicely; I've tested it with both Alistair's test stream and a real signal, and I'm getting a consistent 25fps out of the VBI with or without xawtv grabbing, and the test stream looks good to me. So, Tested-by: Dr. David Alan Gilbert <dave@treblig.org> Thanks for fixing this! Dave > --- > drivers/media/common/videobuf2/videobuf2-core.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c > index 8c1df829745b..40d89f29fa33 100644 > --- a/drivers/media/common/videobuf2/videobuf2-core.c > +++ b/drivers/media/common/videobuf2/videobuf2-core.c > @@ -2735,9 +2735,14 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read) > return -EBUSY; > > /* > - * Start with count 1, driver can increase it in queue_setup() > + * Start with q->min_buffers_needed + 1, driver can increase it in > + * queue_setup() > + * > + * 'min_buffers_needed' buffers need to be queued up before you > + * can start streaming, plus 1 for userspace (or in this case, > + * kernelspace) processing. > */ > - count = 1; > + count = max(2, q->min_buffers_needed + 1); > > dprintk(q, 3, "setting up file io: mode %s, count %d, read_once %d, write_immediately %d\n", > (read) ? "read" : "write", count, q->fileio_read_once, > -- > 2.42.0 >
On 03/12/2023 17:46, Dr. David Alan Gilbert wrote: > * Hans Verkuil (hverkuil-cisco@xs4all.nl) wrote: >> The vb2 read support requests 1 buffer, leaving it to the driver >> to increase this number to something that works. >> >> Unfortunately, drivers do not deal with this reliably, and in fact >> this caused problems for the bttv driver and reading from /dev/vbiX, >> causing every other VBI frame to be all 0. >> >> Instead, request as the number of buffers whatever is the maximum of >> 2 and q->min_buffers_needed+1. >> >> In order to start streaming you need at least q->min_buffers_needed >> queued buffers, so add 1 buffer for processing. And if that field >> is 0, then choose 2 (again, one buffer is being filled while the >> other one is being processed). >> >> This certainly makes more sense than requesting just 1 buffer, and >> the VBI bttv support is now working again. >> >> It turns out that the old videobuf1 behavior of bttv was to allocate >> 8 (video) and 4 (vbi) buffers when used with read(). After the vb2 >> conversion that changed to 2 for both. With this patch it is 3, which >> is really all you need. >> >> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl> >> Fixes: b7ec3212a73a ("media: bttv: convert to vb2") > > This looks like it's working nicely; I've tested it with both > Alistair's test stream and a real signal, and I'm getting > a consistent 25fps out of the VBI with or without xawtv > grabbing, and the test stream looks good to me. > > So, > > Tested-by: Dr. David Alan Gilbert <dave@treblig.org> > > Thanks for fixing this! Thank you for testing this! Much appreciated. Regards, Hans > > Dave > >> --- >> drivers/media/common/videobuf2/videobuf2-core.c | 9 +++++++-- >> 1 file changed, 7 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c >> index 8c1df829745b..40d89f29fa33 100644 >> --- a/drivers/media/common/videobuf2/videobuf2-core.c >> +++ b/drivers/media/common/videobuf2/videobuf2-core.c >> @@ -2735,9 +2735,14 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read) >> return -EBUSY; >> >> /* >> - * Start with count 1, driver can increase it in queue_setup() >> + * Start with q->min_buffers_needed + 1, driver can increase it in >> + * queue_setup() >> + * >> + * 'min_buffers_needed' buffers need to be queued up before you >> + * can start streaming, plus 1 for userspace (or in this case, >> + * kernelspace) processing. >> */ >> - count = 1; >> + count = max(2, q->min_buffers_needed + 1); >> >> dprintk(q, 3, "setting up file io: mode %s, count %d, read_once %d, write_immediately %d\n", >> (read) ? "read" : "write", count, q->fileio_read_once, >> -- >> 2.42.0 >>
diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c index 8c1df829745b..40d89f29fa33 100644 --- a/drivers/media/common/videobuf2/videobuf2-core.c +++ b/drivers/media/common/videobuf2/videobuf2-core.c @@ -2735,9 +2735,14 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read) return -EBUSY; /* - * Start with count 1, driver can increase it in queue_setup() + * Start with q->min_buffers_needed + 1, driver can increase it in + * queue_setup() + * + * 'min_buffers_needed' buffers need to be queued up before you + * can start streaming, plus 1 for userspace (or in this case, + * kernelspace) processing. */ - count = 1; + count = max(2, q->min_buffers_needed + 1); dprintk(q, 3, "setting up file io: mode %s, count %d, read_once %d, write_immediately %d\n", (read) ? "read" : "write", count, q->fileio_read_once,
The vb2 read support requests 1 buffer, leaving it to the driver to increase this number to something that works. Unfortunately, drivers do not deal with this reliably, and in fact this caused problems for the bttv driver and reading from /dev/vbiX, causing every other VBI frame to be all 0. Instead, request as the number of buffers whatever is the maximum of 2 and q->min_buffers_needed+1. In order to start streaming you need at least q->min_buffers_needed queued buffers, so add 1 buffer for processing. And if that field is 0, then choose 2 (again, one buffer is being filled while the other one is being processed). This certainly makes more sense than requesting just 1 buffer, and the VBI bttv support is now working again. It turns out that the old videobuf1 behavior of bttv was to allocate 8 (video) and 4 (vbi) buffers when used with read(). After the vb2 conversion that changed to 2 for both. With this patch it is 3, which is really all you need. Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl> Fixes: b7ec3212a73a ("media: bttv: convert to vb2") --- drivers/media/common/videobuf2/videobuf2-core.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)