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On 2/14/20 7:23 PM, Sowjanya Komatineni wrote:
Tegra210 contains a powerful Video Input (VI) hardware controller
which can support up to 6 MIPI CSI camera sensors.
Each Tegra CSI port can be one-to-one mapped to VI channel and can
capture from an external camera sensor connected to CSI or from
built-in test pattern generator.
Tegra210 supports built-in test pattern generator from CSI to VI.
This patch adds a V4L2 media controller and capture driver support
for Tegra210 built-in CSI to VI test pattern generator.
Signed-off-by: Sowjanya Komatineni <skomatineni@xxxxxxxxxx>
---
drivers/staging/media/Kconfig | 2 +
drivers/staging/media/Makefile | 1 +
drivers/staging/media/tegra/Kconfig | 10 +
drivers/staging/media/tegra/Makefile | 8 +
drivers/staging/media/tegra/TODO | 10 +
drivers/staging/media/tegra/tegra-common.h | 239 +++++++
drivers/staging/media/tegra/tegra-csi.c | 374 ++++++++++
drivers/staging/media/tegra/tegra-csi.h | 115 ++++
drivers/staging/media/tegra/tegra-vi.c | 1019
++++++++++++++++++++++++++++
drivers/staging/media/tegra/tegra-vi.h | 79 +++
drivers/staging/media/tegra/tegra-video.c | 118 ++++
drivers/staging/media/tegra/tegra-video.h | 32 +
drivers/staging/media/tegra/tegra210.c | 767
+++++++++++++++++++++
drivers/staging/media/tegra/tegra210.h | 190 ++++++
14 files changed, 2964 insertions(+)
create mode 100644 drivers/staging/media/tegra/Kconfig
create mode 100644 drivers/staging/media/tegra/Makefile
create mode 100644 drivers/staging/media/tegra/TODO
create mode 100644 drivers/staging/media/tegra/tegra-common.h
create mode 100644 drivers/staging/media/tegra/tegra-csi.c
create mode 100644 drivers/staging/media/tegra/tegra-csi.h
create mode 100644 drivers/staging/media/tegra/tegra-vi.c
create mode 100644 drivers/staging/media/tegra/tegra-vi.h
create mode 100644 drivers/staging/media/tegra/tegra-video.c
create mode 100644 drivers/staging/media/tegra/tegra-video.h
create mode 100644 drivers/staging/media/tegra/tegra210.c
create mode 100644 drivers/staging/media/tegra/tegra210.h
<snip>
+/*
+ * videobuf2 queue operations
+ */
+static int tegra_channel_queue_setup(struct vb2_queue *vq,
+ unsigned int *nbuffers,
+ unsigned int *nplanes,
+ unsigned int sizes[],
+ struct device *alloc_devs[])
+{
+ struct tegra_vi_channel *chan = vb2_get_drv_priv(vq);
+
+ if (*nplanes)
+ return sizes[0] < chan->format.sizeimage ? -EINVAL : 0;
+
+ *nplanes = 1;
+ sizes[0] = chan->format.sizeimage;
+ alloc_devs[0] = chan->vi->dev;
+
+ /*
+ * allocate min 3 buffers in queue to avoid race between DMA
+ * writes and userspace reads.
+ */
+ if (*nbuffers < 3)
+ *nbuffers = 3;
First of all, don't check this here, instead set the struct vb2_queue
field
'min_buffers_needed' to 3 instead.
But the reason given for this check is peculiar: there should not be any
race at all. Usually the reason for requiring a specific minimum
number of
buffers is that the DMA engine needs at least 2 buffers before it can
start
streaming: it can't give back a buffer to userspace (vb2_buffer_done())
unless there is a second buffer it can start to capture to next. So
for many
DMA implementations you need a minimum of 2 buffers: two buffers for the
DMA engine, one buffer being processed by userspace.
If the driver is starved of buffers it will typically keep capturing to
the last buffer until a new buffer is queued.
In any case, once the driver releases a buffer via vb2_buffer_done() the
buffer memory is no longer owned by the driver.
To be precise, buffer ownership is as follows:
userspace -> VIDIOC_QBUF -> vb2 -> buf_queue -> driver ->
vb2_buffer_done() -> vb2 -> VIDIOC_DQBUF -> userspace
(vb2 == videobuf2 framework)
Note that vb2 never touches the buffer memory.
So if you get a race condition in this driver, then there is something
strange going on. It looks like vb2_buffer_done() is called while DMA is
still ongoing, or because the driver really needs to keep one buffer
available at all times.
Regards,
Hans
