On 2/16/20 3:03 AM, Hans Verkuil wrote:
External email: Use caution opening links or attachments
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
Thanks Hans.
On running v4l2-compliance streaming tests for longer run, I noticed
kernel reporting unable to write to read-only memory and with debugs I
observed when this error was reported, I see 2 buffers queued and both
using same address.
for first buffer capture start thread initiates capture and wakes done
thread to wait for memory write ack and once its done buffer is released
to user space but I see upon buffer released to user space immediate
next buffer capture single shot gets issued (as soon as single shot is
issued frame capture data is written to memory by DMA) and I see this
kernel error of unable to write to read-only memory.
This error happens rare and happens on long run and all the times of
repro's, I see when other thread releases buffer immediate I see single
shot gets issued as 2 buffers are queued up at the same time with same
DMA address.
With using minimum 3 buffers, this issue doesnt happen at all from
almost 72 hours of testing.
Will try with setting vb2 queue field min_buffers_needed as 3 instead of
adding check in queue setup.
+
+ return 0;
+}
