Re: [RFC PATCH v3 4/6] media: tegra: Add Tegra210 Video input driver
From: Sowjanya Komatineni
Date: Mon Feb 17 2020 - 20:00:01 EST
On 2/17/20 12:04 AM, Hans Verkuil wrote:
External email: Use caution opening links or attachments
On 2/16/20 9:22 PM, Sowjanya Komatineni wrote:
On 2/16/20 12:11 PM, Sowjanya Komatineni wrote:
On 2/16/20 11:54 AM, Sowjanya Komatineni wrote:
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 |ÂÂÂ 2 +
drivers/staging/media/Makefile |ÂÂÂ 1 +
drivers/staging/media/tegra/Kconfig |ÂÂ 10 +
drivers/staging/media/tegra/Makefile |ÂÂÂ 8 +
drivers/staging/media/tegra/TODO |ÂÂ 10 +
drivers/staging/media/tegra/tegra-common.h |Â 239 +++++++
drivers/staging/media/tegra/tegra-csi.c |Â 374 ++++++++++
drivers/staging/media/tegra/tegra-csi.h |Â 115 ++++
drivers/staging/media/tegra/tegra-vi.c | 1019
++++++++++++++++++++++++++++
drivers/staging/media/tegra/tegra-vi.h |ÂÂ 79 +++
drivers/staging/media/tegra/tegra-video.c |Â 118 ++++
drivers/staging/media/tegra/tegra-video.h |ÂÂ 32 +
drivers/staging/media/tegra/tegra210.c |Â 767
+++++++++++++++++++++
drivers/staging/media/tegra/tegra210.h |Â 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.
Just to be clear, I meant all the times when kernel reports error
unable to write to read-only memory, I see 2 buffers gets queued and
as the capture start thread and done thread are parallel and when
capture thread wakes done thread on receiving FS event, done thread
for waiting for memory write happens parallel to next frame capture
and I see while vb2_buffer_done happens in done thread next frame
single shot has been issues by capture start thread in parallel when
it hits this error.
For low latency, we use 2 threads one thread for capture and wait for FS
and on receiving FS even wakes other done thread to wait for memory
write to finish.
While other done thread waits for memory write to finish, capture thread
can start capture for next frame and as soon as single shot is issued
capture frame is written to memory and as this thread runs in parallel
to done thread
there is a possibility vb2_buffer_done being called by
kthread_capture_done while DMA is ongoing by kthread_capture_start and I
observed same DMA address being used got both buffers that got queued at
same time when it hits this error.
"buffers that got queued": you mean that tegra_channel_buffer_queue() is
called twice with different buffers (i.e. with different buffer index values)
but with the same DMA address?
yes I see buf_queue invoked twice and both using same DMA address.
I did not monitored buf index when I repro'd with debugs.
That should not happen (unless the first buffer was returned with
vb2_buffer_done() before the second buffer was queued).
Can you provide more details? E.g. buffer index, memory model used when
streaming, total number of buffers allocated by REQBUFS.
memory type is MMAP. buffer count is 1. Didn't monitored buf index but
when this happened as count is 1 so I think it might be index 0.
But what I noticed is on running long hours rarely this repro's and at
the time of repro, I see 2 immediate buf_queue with same DMA address.
1st buffer capture starts and received FS and wakes other thread to wait
for MW_ACK_DONE and when capture thread executes for 2nd buffer right as
soon as single shot bit is set which writes captured data to memory
kernel error of unable to write to read-only memory happens.
I couldn't add more debugs to confirm if 1st buffer release finished or
not by the time 2nd buffer single shot is issued but I see MW_ACK_DONE
event received for 1st buffer.
Adding more debugs does not repro this kernel error and that could be
because delays with debug messages helps time interval b/w buffer
release and next buffer single shot.
I would like to fully understand this. Just increasing the minimum number
of buffers, while reasonable by itself, *does* feel like it is just
hiding the symptoms.
Regards,
Hans
kthread for capture start and kthread for done which waiting for memory
write to happen runs in parallel.
Its hard to confirm if buffer done is invoked by kthread_done at same
time of kthread_capture DMA write of next frame as adding debugs has
impact on delay and doesnt repro with more debugs.
But just increasing no.of min buffers to 3 doesnt repro at all and I
never see 2 buffer queue requests with same DMA address as min buffers
are 3.
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;
+}