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Subject: Re: [RFC PATCH 0/5] Apple Macs machine-level ASoC driver
From:   =?utf-8?Q?Martin_Povi=C5=A1er?= <povik@cutebit.org>
In-Reply-To: <YmKeEKa0w2xLM9cL@sirena.org.uk>
Date:   Fri, 22 Apr 2022 14:36:03 +0200
Cc:     =?utf-8?Q?Martin_Povi=C5=A1er?= <povik+lin@cutebit.org>,
        Liam Girdwood <lgirdwood@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzk+dt@kernel.org>,
        Jaroslav Kysela <perex@perex.cz>,
        Takashi Iwai <tiwai@suse.com>, alsa-devel@alsa-project.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        Mark Kettenis <kettenis@openbsd.org>,
        Hector Martin <marcan@marcan.st>,
        Sven Peter <sven@svenpeter.dev>
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To:     Mark Brown <broonie@kernel.org>
Precedence: bulk


> On 22. 4. 2022, at 14:22, Mark Brown <broonie@kernel.org> wrote:
>=20
> On Fri, Apr 22, 2022 at 01:44:06PM +0200, Martin Povi=C5=A1er wrote:
>=20
>>> So previously each speaker would get two slots but now it just gets =
one?
>=20
>> No the other way around. Previously (with the driver as it is RFCed),
>> each speaker gets a single slot, and 'Left', 'Right' and =
=E2=80=98LeftRight'
>> 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).
>=20
>> 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.
>=20
> 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=E2=80=99s 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/so=
und/soc/codecs/tas2770.c#n416