Messages in this thread | | | Subject | Re: [PATCH 0/4] media: platform: Add Aspeed Video Engine driver | From | Eddie James <> | Date | Thu, 13 Sep 2018 14:11:49 -0500 |
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On 09/03/2018 06:57 AM, Hans Verkuil wrote: > Hi Eddie, > > Thank you for your work on this. Interesting to see support for this SoC :-) > > On 08/29/2018 11:09 PM, Eddie James wrote: >> The Video Engine (VE) embedded in the Aspeed AST2400 and AST2500 SOCs >> can capture and compress video data from digital or analog sources. With >> the Aspeed chip acting as a service processor, the Video Engine can >> capture the host processor graphics output. >> >> This series adds a V4L2 driver for the VE, providing a read() interface >> only. The driver triggers the hardware to capture the host graphics output >> and compress it to JPEG format. >> >> Testing on an AST2500 determined that the videobuf/streaming/mmap interface >> was significantly slower than the simple read() interface, so I have not >> included the streaming part. > Do you know why? It should be equal or faster, not slower.
Yes, it seems to be an issue with the timing of the video engine interrupts compared with how a normal v4l2 application queues buffers. With the simple read() application, the driver can swap between DMA buffers freely and get a frame ahead. With the streaming buffers, I found the driver ran through the queue quite quickly, but then, once userspace queues again, we had to wait for the next frame, as I couldn't get a frame ahead since no buffers were available during that time period. This could possibly be solved with more buffers but this gets to require a lot of memory, since each buffer is allocated for the full frame size even though we only fill a fraction of it with JPEG data...
> > I reviewed about half of the driver, but then I stopped since there were too > many things missing. > > First of all, you need to test your driver with v4l2-compliance (available here: > https://git.linuxtv.org/v4l-utils.git/). Always compile from the git repo since > the versions from distros tend to be too old. > > Just run 'v4l2-compliance -d /dev/videoX' and fix all issues. Then run > 'v4l2-compliance -s -d /dev/videoX' to test streaming. > > This utility checks if the driver follows the V4L2 API correctly, implements > all ioctls that it should and fills in all the fields that it should. > > Please add the output of 'v4l2-compliance -s' to future versions of this patch > series: I don't accept V4L2 drivers without a clean report of this utility.
Sure thing. Thanks for the guidance.
> > If you have any questions, then mail me or (usually quicker) ask on the #v4l > freenode irc channel (I'm in the CET timezone). > > One thing that needs more explanation: from what I could tell from the driver > the VIDIOC_G_FMT ioctl returns the detected format instead of the current > format. This is wrong. Instead you should implement the VIDIOC_*_DV_TIMINGS > ioctls and the V4L2_EVENT_SOURCE_CHANGE event. > > The normal sequence is that userspace queries the current timings with > VIDIOC_QUERY_DV_TIMINGS, if it finds valid timings, then it sets these > timings with _S_DV_TIMINGS. Now it can call G/S_FMT. If the timings > change, then the driver should detect that and send a V4L2_EVENT_SOURCE_CHANGE > event.
OK I see. I ended up simplifying this part anyway since it's not possible to change the video size from the driver. I don't think there is a need for VIDIOC_QUERY_DV_TIMINGS now, but feel free to review.
Thanks again, Eddie
> > When the application receives this event it can take action, such as > increasing the size of the buffer for the jpeg data that it reads into. > > The reason for this sequence of events is that you can't just change the > format/resolution mid-stream without giving userspace the chance to > reconfigure. > > Regards, > > Hans > >> It's also possible to use an automatic mode for the VE such that >> re-triggering the HW every frame isn't necessary. However this wasn't >> reliable on the AST2400, and probably used more CPU anyway due to excessive >> interrupts. It was approximately 15% faster. >> >> The series also adds the necessary parent clock definitions to the Aspeed >> clock driver, with both a mux and clock divider. >> >> Eddie James (4): >> clock: aspeed: Add VIDEO reset index definition >> clock: aspeed: Setup video engine clocking >> dt-bindings: media: Add Aspeed Video Engine binding documentation >> media: platform: Add Aspeed Video Engine driver >> >> .../devicetree/bindings/media/aspeed-video.txt | 23 + >> drivers/clk/clk-aspeed.c | 41 +- >> drivers/media/platform/Kconfig | 8 + >> drivers/media/platform/Makefile | 1 + >> drivers/media/platform/aspeed-video.c | 1307 ++++++++++++++++++++ >> include/dt-bindings/clock/aspeed-clock.h | 1 + >> 6 files changed, 1379 insertions(+), 2 deletions(-) >> create mode 100644 Documentation/devicetree/bindings/media/aspeed-video.txt >> create mode 100644 drivers/media/platform/aspeed-video.c >>
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