On 10/23/2012 11:17 AM, Tomi Valkeinen wrote:
On 2012-10-23 18:42, Ricardo Neri wrote:
What registers does the audio side need to access?
It only needs access to the DMA audio data port. All other operations
that the audio driver needs are done through the omapdss audio interface.
Hmm, so the audio side only needs the address of one register, for the
audio data, and this address is given to sDMA? You have
OMAP_HDMI_AUDIO_DMA_PORT in the audio code, is it the HDMI_WP_AUDIO_DATA
register?
Yes, that is the register it needs.
If so, you could pass only that one address, instead of the whole HDMI
register space?
Yes, that could work. I thought about that but the common HDMI driver
would have to know the the IP-specific register, which it should not.
Perhaps the IP-specific register address can be passed by a IP-specific
function such as hdmi_get_audio_dma_port for the common HDMI driver to
populate the resource.
Btw, could this be another reason to convert the IP-specific libraries
to drivers?
My point here is that we should make it very clear what the audio side
can access. If we pass the whole HDMI register space, we should, in
theory, be prepared to cope with the audio driver changing any register
there. But if we pass only one register (or certain small ranges), we
know the rest of the registers are safe.
True.
Why are part of the
registers accessed via the hdmi driver API, and some directly? I imagine
it'd be better to do either one of those, but not both.
This is because in the current omapdss audio interface we have no
functionality to handle the DMA transfers for audio. Do you think it
would be good to explore implementing support for that? At this point it
is not clear for me how to do it without duplicating the functionality
that ASoC provides for that.
No, if the common ASoC code provides functionality for this, we should
at least try to use it.
I was looking at the ti_hdmi_4xxx_ip.h, searching for audio related
registers by searching "AUD" string. I don't know if it makes any sense
(you're better to have a say on that), but I think we could pass some of
the audio registers ranges to the audio driver for use.
For example, the HDMI_WP_AUDIO_* registers are together, we could give
those to the audio driver if it makes sense. HDMI_CORE_AV_AUD* registers
are a bit scattered, but... I guess it wouldn't be difficult to pass
those also, there's still only a couple separate ranges.
Even though this would allow our HDMI drivers to be more inline with
what other HDMI drivers do, things like power management and interrupts
are still handled by DSS, unlike x86, for instance [1][2]. So the audio
drivers will still depend on DSS. Also, the register layout is different
for OMAP5 and audio registers are even more scattered. Furthermore, the
common HDMI driver would have to know the IP-specific layout to know
what register spaces expose to the audio driver (another reason to have
IP-specific drivers?). So I would vote for continuing using the omapdss
audio interface.
But I also have no problem with having the hdmi audio API in the hdmi
video driver, as we do now. And I think we in any case need a few
functions, even if we would give the audio driver access to the AUD
registers.
Yes, interrupt handling, for instance.
BR,
Ricardo
[1].http://www.spinics.net/lists/linux-omap/msg75969.html
[2]. http://www.spinics.net/lists/linux-omap/msg75968.html
Tomi
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