linux-kernel - Re: [PATCH 0/2] Graph fixes for using multiple endpoints per port

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Date:   Thu, 13 Dec 2018 08:53:38 +0200
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Tony Lindgren <tony@...mide.com>
CC:     Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
        Sebastian Reichel <sre@...nel.org>,
        Jarkko Nikula <jarkko.nikula@...mer.com>
Subject: Re: [PATCH 0/2] Graph fixes for using multiple endpoints per port



On 12/12/2018 16.50, Tony Lindgren wrote:
> * Peter Ujfalusi <peter.ujfalusi@...com> [181212 13:03]:
>> On 12/12/2018 2.19, Tony Lindgren wrote:
>>> In my McBSP case there is only a single physical I2S port
>>> that can be TDM split into timeslots.
>>
>> So what is missing from the McBSP driver is to configure the TDM. We
>> never had a hardware which would require it so it is _not_ implemented.
> 
> Curiously.. Nothing needs to be done in the McBSP driver for the droid
> 4 TDM configuration AFAIK.

So you always have 4 timeslot and that's it?

> The CPCAP PMIC is the clock master, and only the PMIC registers need to
> be configured in this case for the timeslot to switch between codecs
> connected to McBSP3.

The McBSP TDM configuration is not master only.
You basically tell McBSP on which timeslot to transmit/receive.
Let's say you have two codecs connected to a single McBSP.
codec1 is configured to listen for timeslot 0/1
codec2 is configured to listen for timeslot 2/3

If you open a stereo stream to codec1 then you tell McBSP to
send/receive the data under timeslot 0/1 and ignore any other timeslots.

If you open a stereo stream to codec2 then you tell McBSP to
send/receive the data under timeslot 2/3 and ignore any other timeslots.

For codec1 you don't really need anything regarding to TDM configuration
as McBSP will send/receive right after the start condition on the FS,
but for codec2 you need to configure the TDM mode of McBSP to ignore
timeslot 0/1

>> imho the 'only' thing is to implement the set_tdm_slot callback for the
>> McBSP DAI. In DT you would have single card with two dai_link section
>> and each section would set different tdm slots to use for the codecs
>> listening on different slots.
>>
>> There is one issue for sure with this setup: the two PCM can not be used
>> at the same time. But we have one DMA channel so if you would open both
>> the PCM stream need to be set up in a way to match with the HW or create
>> a asound.conf file to do some mapping.
> 
> Yes in the droid 4 TDM case only one device can be used at a time
> and all that configuration is done in the PMIC codec .set_tdm_slot
> function.

Hrm, do you have two DAIs on the PMIC side or different timeslots from
the TDM stream is routed to different outputs, similarly to twl6040
where timeslot 0/1 is Headset, timeslot 2/3 is Handsfree and timeslot 5
is to drive a vibra?

> I think it's possible to do more complex configurations where McBSP
> is the master and would implement a .set_tdm_slot function. But I
> don't know anything about that and I'm not aware of any such use
> cases in the mainline kernel.

No, the set_tdm_slot is applicable for both master and slave mode of McBSP.

> 
> Regards,
> 
> Tony
> 

- Péter

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