linux-kernel - Re: [PATCH v3 01/10] ARM: tegra: Set the sound card model that alsaucm expects

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Date:	Wed, 04 Feb 2015 09:56:26 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexandre Courbot <gnurou@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Andrew Bresticker <abrestic@...omium.org>,
	Simon Glass <sjg@...omium.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Kumar Gala <galak@...eaurora.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Dylan Reid <dgreid@...omium.org>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 01/10] ARM: tegra: Set the sound card model that alsaucm
 expects

On 02/04/2015 02:13 AM, Tomeu Vizoso wrote:
> On 02/03/2015 05:35 PM, Stephen Warren wrote:
>> On 02/03/2015 06:13 AM, Tomeu Vizoso wrote:
>>> On 2 February 2015 at 22:08, Stephen Warren <swarren@...dotorg.org> wrote:
>>>> On 01/28/2015 03:50 AM, Tomeu Vizoso wrote:
>>>>>
>>>>> Patches are on its way to add a config file to alsaucm for the Nyan
>>>>> boards. Use the same card ID that alsaucm will expect.
>>>>
>>>>
>>>>> diff --git a/arch/arm/boot/dts/tegra124-nyan-big.dts
>>>>> b/arch/arm/boot/dts/tegra124-nyan-big.dts
>>>>
>>>>
>>>>>           sound {
>>>>> -               compatible = "nvidia,tegra-audio-max98090-nyan-big",
>>>>> +               compatible = "nvidia,tegra-audio-max98090-nyan",
>>>>>                                "nvidia,tegra-audio-max98090";
>>>>
>>>>
>>>> I'm not convinced that removing the board-specific compatible value is a
>>>> great idea. What if we find we need to distinguish between different boards
>>>> that use this same binding in the future. That situation is exactly why we
>>>> have board-/SoC-specific values in compatible even if we don't immediately
>>>> use them.
>>>
>>> I understand the need of naming each component variant so they can be
>>> distinguished in the future, but in this case it's the exact same hw.
>>
>> That's not true. These are two different boards that are derived from
>> the same base design. The intent may be that they are the same, but the
>> whole point of board-specific compatible values is to cover the case
>> where mistakes and exceptions appear later.
>
> Fair enough.
>
>>>>> -               nvidia,model = "Acer Chromebook 13";
>>>>> +               nvidia,model = "GoogleNyan";
>>>>
>>>>
>>>> I believe this also technically breaks ABI, since some user-space tools use
>>>> the model to look up saved state. Can we not leave this as is, and just have
>>>> the UCM files know about both names?
>>>
>>> Well, "A13" isn't a great card id. Given that there's no users yet, I
>>> would prefer to take this chance to put a sane value in there. Btw,
>>> alsa-lib has now a UCM config for this and it uses the GoogleNyan card
>>> id (has been picked up already by OpenSUSE).
>>
>> "A13" didn't appear anywhere, did it? Perhaps that was a shorthand for
>> "Acer Chromebook 13". Yes, I agree we should use the user-visible model
>> number here; "Acer CB5" or perhaps "Acer CB5-xxx" whatever xxx actually is.
>
> Ok, so we can go with Acer-CB5-311 for the nyan big.
>
> Unfortunately there doesn't exist a single product id that corresponds
> with the nyan blaze, but at least four: K4K83UA, K4K11UA, K4K78UA and
> K4K23UA. The commercial name of the series that contain a blaze board is
> "HP Chromebook 14 G3", but that doesn't fit in the card id field (16 byte).

Oh, the 16-byte limit is rather annoying:-( Some of our existing DT 
files don't fit into that limit.

> What do you think of using GoogleNyanBig and GoogleNyanBlaze? Or maybe
> just NyanBig and NyanBlaze? IMO it's more important that the card ids
> correspond 1-to-1 to the hw than their recognizability, as it's not
> something that end users will be messing with.

I'm not entirely sure that the user won't ever see those values; don't 
some X11 GUI tools display them? Still, as you say there isn't too much 
we can do, so since these names are unique/complete I figure they're OK.
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