On 01/22/2015 09:07 AM, Jean-Francois Moine wrote:
On Wed, 21 Jan 2015 21:14:07 +0100
Lars-Peter Clausen <lars@xxxxxxxxxx> wrote:
[...]
+ card->dai_link->dai_fmt =
+ snd_soc_of_parse_daifmt(of_cpu, "dt-audio-card,",
+ NULL, NULL) &
+ ~SND_SOC_DAIFMT_MASTER_MASK;
This one does not seem to be in the bindings documentation.
Sorry, I forgot to remove it from the patch.
Ah, too bad this was the part I was most interested in. I think that using
the generic of graph framework as a unified way for expressing non-control
links is a good idea, whether it be for audio, video or something else.
But I think there are some open questions that need to be address when
coming up with a specification for audio so we do not have to write yet
another incompatible DT spec in 3 months time.
One issue is how to deal with multi-point-to-multi-point links. I2S/TDM is a
bus and can have more than one reader/writer.
The second issue is how to describe the clock and frame master
relationships. Multiple different buses can share the same clock and frame
generator. E.g. typically the capture and playback stream are linked in this
way.
How are we going to handle bus specific properties. Properties which are
neither a property of either of the endpoints on the link, but of the link
itself.
BTW, the graph of port should also contain pieces of the audio specific
hardware information as the ones found in the simple-card (clock,
GPIO, ...). This information could be written as generic device node
properties. i.e without any prefix.
I was also wondering about some of these properties, as widgets and
routing. They seem to be software information and Linux specific.
Must these properties appear in the DTs?
Well last time I checked the speaker on my board was hardware not software
and wasn't Linux specific either ;) Those widgets and routing represent the
(typically analog) audio fabric on the board and are part of the hardware
description. This is not even ASoC or devicetree specific, e.g. HDA uses a
similar concept where the BIOS provides a description of which pins of the
audio CODEC is connected to which speaker, microphone, etc. And especially
on embedded boards the audio fabric can become quite complex.
Your example is a relative simple one where you do not have any additional
audio fabric on the board itself.
- Lars
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