390a71e361
[ Upstream commit 350ab13e1382f2afcc2285041a1e75b80d771c2c ]
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")
Tested-by: Dr. David Alan Gilbert <dave@treblig.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.