linux-kernel - Re: [PATCH 5/8] pwm: stm32-lp: add support for stm32mp25

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Message-ID: <c38324ea-0cf2-49f0-8d3c-2cd0ffd958b2@foss.st.com>
Date: Wed, 26 Feb 2025 19:14:26 +0100
From: Fabrice Gasnier <fabrice.gasnier@...s.st.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
CC: <lee@...nel.org>, <ukleinek@...nel.org>, <alexandre.torgue@...s.st.com>,
        <robh@...nel.org>, <krzk+dt@...nel.org>, <conor+dt@...nel.org>,
        <wbg@...nel.org>, <jic23@...nel.org>, <daniel.lezcano@...aro.org>,
        <tglx@...utronix.de>, <catalin.marinas@....com>, <will@...nel.org>,
        <devicetree@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <linux-iio@...r.kernel.org>, <linux-pwm@...r.kernel.org>,
        <olivier.moysan@...s.st.com>
Subject: Re: [PATCH 5/8] pwm: stm32-lp: add support for stm32mp25

On 2/26/25 08:54, Krzysztof Kozlowski wrote:
> On 25/02/2025 15:58, Fabrice Gasnier wrote:
>>
>>
>> On 2/25/25 13:04, Krzysztof Kozlowski wrote:
>>> On Mon, Feb 24, 2025 at 07:01:47PM +0100, Fabrice Gasnier wrote:
>>>>  	}
>>>>  
>>>>  	return pinctrl_pm_select_sleep_state(dev);
>>>> @@ -246,6 +413,7 @@ static DEFINE_SIMPLE_DEV_PM_OPS(stm32_pwm_lp_pm_ops, stm32_pwm_lp_suspend,
>>>>  
>>>>  static const struct of_device_id stm32_pwm_lp_of_match[] = {
>>>>  	{ .compatible = "st,stm32-pwm-lp", },
>>>> +	{ .compatible = "st,stm32mp25-pwm-lp", },
>>>
>>> No driver data suggests device is backwards compatible. Commit msg
>>> suggests not, so that's confusing.
>>
>>
>> The LPTimer PWM driver takes benefit of the MFD parent driver to feed in
>> data, e.g. 'num_cc_chans'. Number of channels is now variable, on
> 
> This means this ID table is useless. You do the matching via parent
> device, so stop growing the table and call it deprecated or something.
> 
>> STM32MP25 (e.g. not a single channel). But it can't be hard-coded as
>> compatible data. (there's only 1 channel on earlier LP Timer hardware
>> revision).
>>
>> The hardware controller is a bit different, hence the new compatible
> 
> If it works with old compatible, it's an easy proof that it is
> compatible, so please counter argument that with something specific.

Ack, I'll drop the "st,stm32mp25-pwm-lp" compatible, as match through
the parent device is achieved here.
Alternatively, reading directly the hardware configuration register
could be used to retrieve the 'num_cc_chans'.

Thanks for reviewing,
Best regards,
Fabrice
> What is different that driver cannot work with new device using old
> interface or old features?
> 
> 
> Best regards,
> Krzysztof