linux-kernel - Re: [PATCH v3 1/4] ASoC: dt-bindings: lpc32xx: Add lpc32xx i2s DT binding

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Date: Mon, 17 Jun 2024 17:48:42 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Piotr Wojtaszczyk <piotr.wojtaszczyk@...esys.com>
Cc: Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Vladimir Zapolskiy <vz@...ia.com>,
 Russell King <linux@...linux.org.uk>, Jaroslav Kysela <perex@...ex.cz>,
 Takashi Iwai <tiwai@...e.com>, "J.M.B. Downing"
 <jonathan.downing@...tel.com>, Arnd Bergmann <arnd@...db.de>,
 Chancel Liu <chancel.liu@....com>, Michael Ellerman <mpe@...erman.id.au>,
 linux-sound@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 alsa-devel@...a-project.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v3 1/4] ASoC: dt-bindings: lpc32xx: Add lpc32xx i2s DT
 binding

On 17/06/2024 16:04, Piotr Wojtaszczyk wrote:
>>
>>> It's used by snd_soc_dai_init_dma_data() in [PATCH v3 4/4] to give the
>>> dmaengine a
>>> hint which dma config to use. The LPC32xx doesn't have yet a dmamux driver like
>>
>> and if I change driver platform data to foo and bar, does the DTS work? No.
> 
> They shouldn't change the same way as expected dma-names shouldn't change.
> Lots of drivers expect the dma-names to be "rx", "tx"
> 
>>
>>> lpc18xx-dmamux.c therefore it still uses platform data entries for
>>> pl08x dma channels
>>> and 'SND_DMAENGINE_PCM_FLAG_NO_DT | SND_DMAENGINE_PCM_FLAG_COMPAT'
>>> flags in the devm_snd_dmaengine_pcm_register().
>>> Typically instead of this platform data you would use regular 'dma'
>>> and 'dma-names' if it had
>>> proper dmamux driver like lpc18xx-dmamux.c
>>
>> Exactly. Use these.
> 
> Then I need to write a lpc32xx dma mux driver, device tree binding for
> it and adjust the
> LPC32xx I2S driver for it. Is this a hard requirement to accept this
> patch set for the
> legacy LPC32xx SoC?

I do not see at all analogy with dma-names. dma-names are used ONLY by
the consumer to pick up proper property "dmas" from DT. They are not
passed to DMA code. They are not used to configure DMA provider at all.

You parse string from DT and pass it further as DMA filtering code. This
is abuse of hardware description for programming your driver and their
dependencies.

Why you cannot hard-code them?

Sorry, to be clear: NAK

> 
>>
>>>
>>>>
>>>> Drop.
>>>>
>>>>
>>>>> +
>>>>> +  "#sound-dai-cells":
>>>>> +    const: 0
>>>>> +
>>>
>>> The "dai-common.yam" doesn't declare a default value for this so
>>
>> Where is my comment to which you refer to? Please do not drop context
>> from replies. I have no clue what you want to discuss here.
> Well I didn't remove the context, you said:
> "
> Drop.
> (...)
> +  "#sound-dai-cells":
> +    const: 0
> "
> So I'm confused whether the "#sound-dai-cells" should be in the dt
> binding or not.

??? Drop is above the text so why do you refer to dai cells? We use here
text-based mailing list style of discussions, not corporate MS Office.

Best regards,
Krzysztof