On 10/06/15 12:23, Arnaud Pouliquen wrote:
Hello Jyri,
Thanks your feedback, my answers in line
On 10/05/2015 03:27 PM, Jyri Sarha wrote:
On 10/01/15 19:50, Arnaud Pouliquen wrote:
Version 2:
This version integrates missing features upgraded to be aligned when
possible
with patch set:
[PATCH RFC v4 0/8] Implement generic ASoC HDMI codec and use it in
tda998x
There are still some details I would like to change if we decide to go
the drm audio bridge way. But before all that, I would like to ask,
why should we go forward with your approach? Is there anything that
can be done with your approach, but can not be done with mine?
Don't take me wrong, I do not see anything fundamentally wrong with
your approach. I would just like hear some justification why we should
abandon my approach - that I've been working on for some time - and go
forward with yours.
Both implementations are similar in term of feature. And i think both
have advantages and drawbacks...
The main difference, is that my approach is based on a standard service
client-provider model.
Means that ops are defined by code in charge of providing the service
(DRM) and not by the client (ALSA).
I don't want to impose my implementation but just propose an alternative
that makes sense for me.
My model merely sees a driver providing access to a piece standard HDMI
HW with audio functionality trough ASoC codec DAI API.
In a first step, before going deep in discussion on the approach, it
should be interesting to have maintainers feedback, to be sure that my
approach could make sense from DRM and ALSA point of view.
Absolutely. In the end the maintainers need to make the final decision
any way.
@DRM (and ALSA) maintainers:
Please, could you give a first feedback on such implementation based on
DRM API extension?
Is it something that could be acceptable (or not) from your point of view?
Here is couple of benefits I can name in my approach:
Video side agnostic implementation
The ASoC side does not need to know anything about video side
implementation. There is no real exposure ASoC side internals in
video side either. Even fbdev driver, or some other non DRM video
driver, could use my implementation.
My approach is the reverse: DRM driver does not need to know anything
about audio side. As ALSA is the client of DRM, seems more logical from
my point of view ...
Now if a generic solution must be found for all video drivers, sure,
your solution is more flexible.
But if i well understood fbdev drivers are no more accepted for upstream
(please correct me if I'm wrong).
So i don't know we have to keep fbdev in picture...
I am not promoting fbdev support. I am merely asking if we want to force
all HDMI drivers to implement a drm_bridge if they want to support audio.
- HDMI encoder driver implementations that do not use DRM bridge
abstraction do not need add an extra DRM object just to get the
audio working.
Short comings I see in the current HDMI audio bridge approach:
In its current from the DRM audio bridge abstraction pretends to be a
generic audio abstraction for DRM devices, but the implementation is
quite specific to external HDMI encoders with spdif and/or i2s
interface. There is a lot of HDMI video devices that provide the
digital audio interface (ASoC DAI) directly and there is no need for
anything but dummy codec implementation (if following ASoC
paradigm). Before going forward I think we should at least consider
how this abstraction would serve those devices.
Sorry, but i don't see any difference between both implementations for
this point.In both implementations, ops are called only if defined.
Could you give me name of the drivers you have in mind?
I am not talking about Beaglebone-Black or tda998x here. There are
platforms where video HW provides the digital audio interface for HDMI
audio directly. For instance OMAP4 and OMAP5 (see
sound/soc/omap/omap-hdmi-audio.c and drivers/video/fbdev/omap2/dss/) are
like that.
Also, I am not entirely happy how the drm_audio_bridge_funcs are used
at the moment. The do not map too well to ASoC DAI callbacks and I do
not see too much point in creating a completely new audio-callback
abstraction, that is sligtly incompatible with ALSA, and then
translating alsa callbacks to these new callbacks. I think the
callbacks should map more or less directly ALSA callbacks.
As API is defined in DRM, it seems more logical to match it with the one
defined for video. From my windows, i didn't see any blocking point to
connect codec callback with this API.
But anyway, this API is not freezed, it could be improved with your help.
The most usual things can be made to work with your API too, but the
translation is not the most efficient one and some features are missing,
for instance muting. Also, in ALSA side the prepare and trigger
callbacks are meant to be used only for starting and stopping the audio
stream. The stream is configured before either one of those are called.
With your API each pause+resume from a video client will reconfigure the
audio from the scratch.
Best regards,
Jyri
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