[alsa-devel] Audio Video synchronization for data received from a HDMI receiver chip

Hans Verkuil hverkuil at xs4all.nl
Thu May 19 13:38:21 CEST 2011

>> > Hi Hans,
>> >
>> > I have another doubt regarding the framework choice for the entire
>> > system that I have, especially the video part of the system. The
>> overall
>> > system is similar to the one depicted below:
>> >
>> > HDMI data --> HDMI receiver chip --> Video Port IP on SoC --> System
>> DDR
>> >
>> > HDMI data is received from external world (from say a set-up box or
>> dvd player),
>> > which is fed to the HDMI receiver chip on-board and then parallel
>> data lines feed
>> > this data to a Video Port IP on the SoC which has a DMA master
>> interface and
>> > hence can push the data thus received directly on system DDR.
>> >
>> > Now, I can figure out that there will be two drivers required here:
>> > # HDMI receiver chip driver (which is essentially a v4l2 subdev being
>> controller via I2C)
>> > # Video Port driver (which is a v4l2 bridge driver)
>> >
>> > Is my understanding correct?
>> Yes.
> Thanks for clarifying this.
>> > Are there any HDMI receiver subdev driver and video bridge driver
>> already available which I can
>> > use for reference?
>> Video bridge drivers are easier: examples are in
>> drivers/media/video/s5p-fimc
>> or in drivers/media/video/davinci. Note that you should use the new
>> videobuf2
>> framework instead of the older videobuf framework. s5p-fimc is using
>> vb2 already.
>> but the vpif capture and display drivers in the davinci directory do
>> not.
> I quickly had a look at the s5p-fimc and davinci approaches, but I found
> that
> the video bridge drivers supported in both the Samsung and TI SoCs,
> support video post-processing operations whereas in our case the Video
> Port
> IP performs almost no additional processing and only passes the unpacked
> raw data received from HDMI bus to system DDR via a DMA master interface.

This is similar to the davinci vpif-capture/vpif-display drivers for the
TI dm646x SoCs. Those videoports are also just a DMA engine without video

> So as such these are no format conversion operations(rgb-to-yuv or
> vice-versa),
> image resizing operations (cropping, scaling..) and image quality
> operations
> (filtering, distortion removal) available in the H/W block.
> What should be the correct choice in such a case?

vpif-capture/display drivers are identical in that respect.



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