linux-kernel - Re: [PATCH 13/25] ASoC: dt-bindings: meson: axg-pdm: document 'sysrate' property

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Date: Mon, 18 Mar 2024 11:55:35 +0100
From: Jerome Brunet <jbrunet@...libre.com>
To: Jan Dakinevich <jan.dakinevich@...utedevices.com>
Cc: Jerome Brunet <jbrunet@...libre.com>, Krzysztof Kozlowski
 <krzysztof.kozlowski@...aro.org>, Neil Armstrong
 <neil.armstrong@...aro.org>, Michael Turquette <mturquette@...libre.com>,
 Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh@...nel.org>, Krzysztof
 Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley
 <conor+dt@...nel.org>, Philipp Zabel <p.zabel@...gutronix.de>, Kevin
 Hilman <khilman@...libre.com>, Martin Blumenstingl
 <martin.blumenstingl@...glemail.com>, Liam Girdwood <lgirdwood@...il.com>,
 Mark Brown <broonie@...nel.org>, Linus Walleij <linus.walleij@...aro.org>,
 Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
 linux-amlogic@...ts.infradead.org, linux-clk@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, alsa-devel@...a-project.org,
 linux-sound@...r.kernel.org, linux-gpio@...r.kernel.org,
 kernel@...utedevices.com
Subject: Re: [PATCH 13/25] ASoC: dt-bindings: meson: axg-pdm: document
 'sysrate' property


On Sun 17 Mar 2024 at 18:52, Jan Dakinevich <jan.dakinevich@...utedevices.com> wrote:

> On 3/15/24 13:22, Jerome Brunet wrote:
>> 
>> On Fri 15 Mar 2024 at 11:00, Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:
>> 
>>> On 15/03/2024 00:21, Jan Dakinevich wrote:
>>>> This option allow to redefine the rate of DSP system clock.
>>>
>>> And why is it suitable for bindings? Describe the hardware, not what you
>>> want to do in the driver.
>>>
>>>>
>>>> Signed-off-by: Jan Dakinevich <jan.dakinevich@...utedevices.com>
>>>> ---
>>>>  Documentation/devicetree/bindings/sound/amlogic,axg-pdm.yaml | 4 ++++
>>>>  1 file changed, 4 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/sound/amlogic,axg-pdm.yaml b/Documentation/devicetree/bindings/sound/amlogic,axg-pdm.yaml
>>>> index df21dd72fc65..d2f23a59a6b6 100644
>>>> --- a/Documentation/devicetree/bindings/sound/amlogic,axg-pdm.yaml
>>>> +++ b/Documentation/devicetree/bindings/sound/amlogic,axg-pdm.yaml
>>>> @@ -40,6 +40,10 @@ properties:
>>>>    resets:
>>>>      maxItems: 1
>>>>  
>>>> +  sysrate:
>>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>>> +    description: redefine rate of DSP system clock
>>>
>>> No vendor prefix, so is it a generic property? Also, missing unit
>>> suffix, but more importantly I don't understand why this is a property
>>> of hardware.
>> 
>> +1.
>> 
>> The appropriate way to set rate of the clock before the driver take over
>> is 'assigned-rate', if you need to customize this for different
>> platform.
>> 
>
> It would be great, but it doesn't work. Below, is what I want to see:
>
> 	assigned-clocks =
> 		<&clkc_audio AUD2_CLKID_PDM_SYSCLK_SEL>,
> 		<&clkc_audio AUD2_CLKID_PDM_SYSCLK_DIV>;
> 	assigned-clock-parents =
> 		<&clkc_pll CLKID_FCLK_DIV3>,
> 		<0>;
> 	assigned-clock-rates =
> 		<0>,
> 		<256000000>;
>
> But regardles of this declaration, PDM's driver unconditionally sets
> sysclk'rate to 250MHz and throws away everything that was configured
> before, reparents audio2_pdm_sysclk_mux to hifi_pll and changes
> hifi_pll's rate.
>
> This value 250MHz is declared here:
>
> static const struct axg_pdm_cfg axg_pdm_config = {
> 	.filters = &axg_default_filters,
> 	.sys_rate = 250000000,
> };
>
> The property 'sysrate' is intended to redefine hardcoded 'sys_rate'
> value in 'axg_pdm_config'.

What is stopping you from removing that from the driver and adding
assigned-rate to 250M is the existing platform ?

>
>> Then you don't have to deal with it in the device driver.
>> 
>>>
>>> Best regards,
>>> Krzysztof
>> 
>> 


-- 
Jerome