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

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Date: Sun, 17 Mar 2024 18:52:15 +0300
From: Jan Dakinevich <jan.dakinevich@...utedevices.com>
To: Jerome Brunet <jbrunet@...libre.com>, Krzysztof Kozlowski
	<krzysztof.kozlowski@...aro.org>
CC: 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 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'.

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

-- 
Best regards
Jan Dakinevich