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

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Message-Id: <A1574F30-62D2-467D-A40B-8FD7C6B8BCFA@cutebit.org>
Date:   Fri, 22 Apr 2022 13:44:06 +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 13:33, Mark Brown <broonie@...nel.org> wrote:
> 
> On Fri, Apr 22, 2022 at 01:28:20PM +0200, Martin Povišer wrote:
>>> 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:
> 
>>>> 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:
> 
> ...
> 
>>> 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.
> 
> So previously each speaker would get two slots but now it just gets one?

No the other way around. Previously (with the driver as it is RFCed),
each speaker gets a single slot, and 'Left', 'Right' and ‘LeftRight'
values of the routing control don't do anything different from each
other (well except maybe 'LeftRight' lessens the volume due to how
the chip handles the edge case of mixing down two channels from the
same slot).

With the new arrangement I am proposing, the two speakers in a left-right
pair get both the same two slots, meaning they get to choose one of the
two slots based on the 'Left' 'Right' value of their routing control.