Date: Wed, 28 Feb 2024 08:28:05 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Alexandre Mergnat <amergnat@...libre.com>,
 Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>,
 Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Matthias Brugger
 <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 Lee Jones <lee@...nel.org>, Flora Fu <flora.fu@...iatek.com>,
 Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
 Sumit Semwal <sumit.semwal@...aro.org>,
 Christian König <christian.koenig@....com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>
Cc: linux-sound@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-mediatek@...ts.infradead.org, linux-media@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH 01/18] ASoC: dt-bindings: mediatek,mt8365-afe: Add audio
 afe document

On 27/02/2024 16:18, Alexandre Mergnat wrote:
>>
>>> +    type: boolean
>>> +
>>> +  mediatek,dmic-iir-on:
>>> +    description:
>>> +      Boolean which specifies whether the DMIC IIR is enabled.
>>> +      If this property is not present the IIR is disabled.
>>
>> "is enabled" or "enable it"?
>>
>> You described the desired Linux feature or behavior, not the actual
>> hardware. The bindings are about the latter, so instead you need to
>> rephrase the property and its description to match actual hardware
>> capabilities/features/configuration etc.
> 
> I will rephrase:
> 
> True to enable the Infinite Impulse Response (IIR) filter
> on the digital microphone inputs.

I still don't know why this is DT-specific. You still tell driver what
to do...

> 
>>
>>> +    type: boolean
>>> +
>>> +  mediatek,dmic-irr-mode:
>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>> +    description:
>>> +      Selects stop band of IIR DC-removal filter.
>>> +      0 = Software programmable custom coeff loaded by the driver.
>>
>> Bindings are for hardware, not drivers. Why is this a property of board DTS?
> 
> Actually this is a hardware feature. Mode 1 t 5 are predefined filters. 
> Mode 0, the HW will read some "coef filter registers" to setup the 
> custom filter. the "coef filter regs" are written by the driver. 
> Currently the coef values are hardcoded in the driver.

You don't get the point. Just because you choose some mode it does not
mean is hardware feature for DT. Sampling frequency done by hardware is
also "hardware feature", but do you put it to DT? No.

Explain why this is board-specific, not runtime configuration.

> 
>>
>>> +      1 = 5Hz if 48KHz mode.
>>> +      2 = 10Hz if 48KHz mode.
>>> +      3 = 25Hz if 48KHz mode.
>>> +      4 = 50Hz if 48KHz mode.
>>> +      5 = 65Hz if 48KHz mode.
>>
>> Use proper unit suffixes - hz.
>>
>>
>>> +    enum:
>>> +      - 0
>>> +      - 1
>>> +      - 2
>>> +      - 3
>>> +      - 4
>>> +      - 5
>>> +
>>> +  mediatek,dmic-two-wire-mode:
>>> +    description:
>>> +      Boolean which turns on digital microphone for two wire mode.
>>> +      If this property is not present the two wire mode is disabled.
>>
>> This looks like hardware property, but the naming looks like SW. Again
>> you instruct what driver should do. Standard disclaimer:
>>
>> You described the desired Linux feature or behavior, not the actual
>> hardware. The bindings are about the latter, so instead you need to
>> rephrase the property and its description to match actual hardware
>> capabilities/features/configuration etc.
> 
> Actually this is a hardware feature. This is ALL I have to describe the 
> HW behavior from the datasheet:
> "
> bit name: ul_dmic_two_wire_ctl
> Turns on digital microphone for two wire mode.
> 0: Turn off
> 1: Turn on

That's rather suggestion it is not a description of hardware but you
want driver to do something...

> "
> 
> On the board schematic, SoC and DMIC and linked by 3 pins:
> - clk
> - data0
> - data1
> 
> IMHO, "two-wire-mode" means the HW use 2 pins for data, and the SoC must 
> be aware of that by reading the register value written by the driver, 
> using the value found in the DTS.

So this depends on type of connection of DMIC? Then rephrase description
property like this.

> 
> I don't get why you think it wouldn't be hardware behavior.

Because telling what to write to the registers which is typical sign of
people stuffing to DT whatever they need to configure the hardware.

> 
> Rephrase description:
> "True to enable the two wire mode of the digital microphone"
> Is it better ?

No, because again you describe some sort of mode. If you insist on such
description, then my answer is: it's runtime, so not suitable for DT.
Instead describe what is the hardware problem/configuration, e.g. "DMIC
is connected with only CLK and DATA0, without third pin" etc.

> 
> About the property name, "mediatek,dmic-two-wire-ctl" sound better for you ?

To sound more like a register less like physical characteristic of the
board? No. The name can stay, I don't have better ideas.


Best regards,
Krzysztof

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