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

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Date:   Fri, 22 Apr 2022 14:36:03 +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 14:22, Mark Brown <broonie@...nel.org> wrote:
> 
> On Fri, Apr 22, 2022 at 01:44:06PM +0200, Martin Povišer wrote:
> 
>>> 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.
> 
> Ah, I think the confusion here is that I'm using slot and channel
> interchangably whereas you're saying that previously the driver would
> allocate two channels to each speaker with duplicate data?

I guess you could say that. Not that there’s duplicate data on the I2S
bus, but the speaker amp would previously be configured to look for the
left and right channel in the same TDM slot (see e.g. set_tdm_slot of
tas2770 [0]).  (Each speaker amp drives a single speaker, but it still
has a notion of left and right channel.)

[0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/sound/soc/codecs/tas2770.c#n416