linux-kernel - Re: [RFC PATCH 0/5] Apple Macs machine-level ASoC driver

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Message-Id: <B68302F2-3D77-4065-8A16-A9CC690AE10B@cutebit.org>
Date:   Fri, 22 Apr 2022 13:28:20 +0200
From:   Martin Povišer <povik@...ebit.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     Martin Povišer <povik+lin@...ebit.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mark Kettenis <kettenis@...nbsd.org>,
        Hector Martin <marcan@...can.st>,
        Sven Peter <sven@...npeter.dev>
Subject: Re: [RFC PATCH 0/5] Apple Macs machine-level ASoC driver



> On 22. 4. 2022, at 13:19, Mark Brown <broonie@...nel.org> wrote:
> 
> On Fri, Apr 22, 2022 at 12:43:30PM +0200, Martin Povišer wrote:
> 
>> I looked in the TAS2770 and TAS2764 drivers/datasheets, and to answer
>> the questions we had:
> 
>> * VSENSE/ISENSE output slots are configured independently of audio samples
>>   routing. Kernel drivers configure the slots based on the 'ti,imon-slot-no'
>>   and 'ti,vmon-slot-no' properties of devicetree.
> 
>> * By default codecs transmit Hi-Z for duration of unused slots.
> 
>> So once we supply the devicetree props it should be electrically sound
>> under any configuration of userspace knobs.
> 
> Great, that's a relief.
> 
>> One final thought on the playback routing controls: On systems with >2
>> speakers, the codecs need to be assigned slots through set_tdm_slot.
>> The macaudio driver RFCed here assigns a single slot to each speaker,
>> making the effect of each speaker's routing control this:
> 
>>  'I2C offset' -- uses a random slot
> 
>>  'Left' 'Right' 'LeftRight' -- uses the single slot we configured
> 
>> I suppose I better assign two slots to speakers in each left-right pair
>> of the same kind (e.g. woofer 1, woofer 2, tweeter). This way the
>> routing control will mimic its behavior from simple stereo systems but
>> replicated within each left-right pair.  (I would prefer to hide the
>> controls altogether, but as I learned that hiding things unless proven
>> dangerous is an ASoC non-goal, this way I can make the controls do
>> something interesting.)
> 
> I don't quite grasp the difference between the arrangement you're
> proposing and assigning a single slot to each speaker?  Possibly it's
> just a reordering of the slots?

Ah, maybe what’s missing is the fact that the way the speaker amp drivers
are written, if they are assigned two slots with a call to set_tdm_slot,
the first slot is considered 'left' and the second is 'right'.

So in the arrangement I am proposing the 'Left', 'Right' and 'LeftRight'
values of the routing control have the nominal effect (within the left-right
speaker pair), while in the other arrangement it is as I described above.