[alsa-devel] [PATCH] ASoC: ti: Allocate dais dynamically for TDM and audio graph card

[Tony Lindgren]

* Peter Ujfalusi <peter.ujfalusi at ti.com> [200212 08:02]:
> 
> 
> On 11/02/2020 19.16, Tony Lindgren wrote:
> > We can have multiple connections on a single McBSP instance configured
> > with audio graph card when using TDM (Time Division Multiplexing). Let's
> > allow that by configuring dais dynamically.
> 
> It is still one DAI...
> If you have multiple codec connected to the same I2S lines, but the
> codecs communicate within different time slots, you still have one DAI
> on the CPU side, but multiple codecs (codec DAIs) with different TDM slot.

OK so subject should say "dodec DAIs" then I guess?

> > See Documentation/devicetree/bindings/sound/audio-graph-card.txt and
> > Documentation/devicetree/bindings/graph.txt for more details for
> > multiple endpoints.
> 
> See the example for 'Multi DAI with DPCM' in audio-graph-card.txt
> The PCM3168a have 2 DAIs: playback and capture, but you can have
> multiple endpoints within a DAI.

Yes this should follow the audio-graph-card.txt example. We end up with
mcbsp3 dts node as below on droid4:

&mcbsp3 {
        #sound-dai-cells = <0>;
        pinctrl-names = "default";
        pinctrl-0 = <&mcbsp3_pins>;
        status = "okay";

        ports {
                mcbsp3_port: port at 0 {
                        #address-cells = <1>;
                        #size-cells = <0>;

                        cpu_dai3: endpoint at 0 {
                                reg = <0>;
                                dai-format = "dsp_a";
                                frame-master = <&cpcap_audio_codec1>;
                                bitclock-master = <&cpcap_audio_codec1>;
                                remote-endpoint = <&cpcap_audio_codec1>;
                        };

                        cpu_dai_mdm: endpoint at 1 {
                                reg = <1>;
                                dai-format = "dsp_a";
                                frame-master = <&cpcap_audio_codec1>;
                                bitclock-master = <&cpcap_audio_codec1>;
                                remote-endpoint = <&mot_mdm6600_audio_codec0>;
                        };
                };
        };
};

That is pretty much the same as the 'Multi DAI with DPCM' example, with
dne dai, and multiple endpoints. I think we still have just one port
for one i2s transport on the mcbsp :)

Does the above look as what you would expect based on the binding?

> > I've tested this with droid4 where cpcap pmic and modem voice are both
> > both wired to mcbsp3. I've also tested this on droid4 both with and
> > without the pending modem audio codec driver that is waiting for n_gsm
> > serdev dependencies to clear.
> 
> What this patch you effectively just creating dummy-dais on top of the
> real McBSP DAI.

Yes I think this is needed for snd-soc-audio-graph-card, and this allows
configuring whatever is needed for the i2s slot. But maybe you have some
better way of doing it in mind?

> You also rename the DAIs, which might break ams-delta.

Oops, that's not good. So should we just keep the old naming if there's
only one endpoint?

> We still have legacy support in
> omap-twl4030.c
> omap3pandora.c
> osk5912.c
> rx51.c
> 
> which will break with the renamed DAI. On the other hand I think the
> legacy support can be dropped from them.

I'm not sure what all that would take.

> I know it was discussed, but can not find the mail:
> Can you brief again on the audio connection?

Below is a link to a mailing list thread where Sebastian describes
the audio connection:

https://lkml.org/lkml/2018/3/28/881

> Do you have branch with working code?

Yeah I have slightly older set of the patches in my droid4-pending-v5.5
kernel.org git branch with voice calls working.

Regards,

Tony