Messages in this thread | | | Subject | Re: [PATCH 0/4] media: platform: Add Aspeed Video Engine driver | From | Eddie James <> | Date | Fri, 14 Sep 2018 10:07:37 -0500 |
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On 09/14/2018 01:56 AM, Hans Verkuil wrote: > On 09/13/2018 09:11 PM, Eddie James wrote: >> >> 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... > For stream I/O you usually need 3 buffers: one is being DMAed, one is > the next queued up frame for the DMA and the third is being processed > in userspace. If userspace doesn't process buffers fast enough, then > the driver will need to capture into the same buffer over and over again > until userspace finally queues another buffer. > > What I don't understand here is what the frame rate is. Is the capture > framerate the same as the host processor graphics output? Or is it > unrelated to that?
Yes, the frame rate is the capture frame rate, unrelated to the host graphics output frame rate. It's really just a bandwidth-saving measure.
> > The problem with read() is that 1) it requires copying the video data, and > 2) you cannot use dmabuf for zero-copying pipelines. Whether or not 2 is > needed depends on your hardware. > >>> 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. > You are capturing the host graphics output, right? So you need to know > the resolution, timings, etc. of that output? What if the host changes > resolution? That's something you need to know, or am I missing something?
Yes, that's why I had those extra lines in set_format, so that if the set format resolution matches the actual frame size, then it can change... I guess I'm probably mis-using the API. Will look into the source event change and timings calls.
> > This is obviously a somewhat different environment than what I am used to, > so bear with me if I ask stupid questions...
No problem!
Thanks, Eddie > > Regards, > > Hans > >> 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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