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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: <YmKPQ6kLCPz+2XTJ@sirena.org.uk>
Date:   Fri, 22 Apr 2022 13:28:20 +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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Message-Id: <B68302F2-3D77-4065-8A16-A9CC690AE10B@cutebit.org>
References: <20220331000449.41062-1-povik+lin@cutebit.org>
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To:     Mark Brown <broonie@kernel.org>
Precedence: bulk


> On 22. 4. 2022, at 13:19, Mark Brown <broonie@kernel.org> wrote:
>=20
> On Fri, Apr 22, 2022 at 12:43:30PM +0200, Martin Povi=C5=A1er wrote:
>=20
>> I looked in the TAS2770 and TAS2764 drivers/datasheets, and to answer
>> the questions we had:
>=20
>> * 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.
>=20
>> * By default codecs transmit Hi-Z for duration of unused slots.
>=20
>> So once we supply the devicetree props it should be electrically =
sound
>> under any configuration of userspace knobs.
>=20
> Great, that's a relief.
>=20
>> 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:
>=20
>>  'I2C offset' -- uses a random slot
>=20
>>  'Left' 'Right' 'LeftRight' -- uses the single slot we configured
>=20
>> 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.)
>=20
> 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=E2=80=99s 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.