linux-kernel - Re: [PATCH 3/3] pwm: axi-pwmgen: add support for external clock

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Message-ID: <dc9c370c-e1e7-4ef9-8738-e6ac8887ee61@baylibre.com>
Date: Wed, 21 May 2025 08:23:14 -0500
From: David Lechner <dlechner@...libre.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Michael Hennerich <michael.hennerich@...log.com>,
 Nuno Sá <nuno.sa@...log.com>,
 Trevor Gamblin <tgamblin@...libre.com>,
 Uwe Kleine-König <ukleinek@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, linux-pwm@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] pwm: axi-pwmgen: add support for external clock

On 5/21/25 5:10 AM, Krzysztof Kozlowski wrote:
> On Tue, May 20, 2025 at 04:00:46PM GMT, David Lechner wrote:
>> Add support for external clock to the AXI PWM generator driver.
>>
>> In most cases, there is a separate external clock that drives the PWM
>> output separate from the peripheral clock. This allows enabling both
>> clocks.
>>
>> Signed-off-by: David Lechner <dlechner@...libre.com>
>> ---
>>  drivers/pwm/pwm-axi-pwmgen.c | 23 ++++++++++++++++++++---
>>  1 file changed, 20 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/pwm/pwm-axi-pwmgen.c b/drivers/pwm/pwm-axi-pwmgen.c
>> index 4337c8f5acf055fc87dc134f2a70b99b0cb5ede6..67992a7561ec0440b1c1fa327f844a0602872771 100644
>> --- a/drivers/pwm/pwm-axi-pwmgen.c
>> +++ b/drivers/pwm/pwm-axi-pwmgen.c
>> @@ -280,9 +280,26 @@ static int axi_pwmgen_probe(struct platform_device *pdev)
>>  	ddata = pwmchip_get_drvdata(chip);
>>  	ddata->regmap = regmap;
>>  
>> -	clk = devm_clk_get_enabled(dev, NULL);
>> -	if (IS_ERR(clk))
>> -		return dev_err_probe(dev, PTR_ERR(clk), "failed to get clock\n");
>> +	/* When clock-names is present, there is a separate ext clock. */
>> +	if (device_property_present(dev, "clock-names")) {
> 
> No. List is ordered, you do not need such dance at all.

I should have added more to the comment here. This is also needed for
backwards compatibility where only what should be the "ext" clock is
given as clocks = <&spi_clk>; and the AXI clock was missing.

> 
>> +		struct clk *axi_clk;
>> +
>> +		axi_clk = devm_clk_get_enabled(dev, "axi");
>> +		if (IS_ERR(axi_clk))
>> +			return dev_err_probe(dev, PTR_ERR(axi_clk),
>> +					     "failed to get axi clock\n");
>> +
>> +		clk = devm_clk_get_enabled(dev, "ext");
> 
> So that's messing the order, which confirms my question from the
> binding.
> 
> No. List has a strict order, you cannot change it just because you want
> to add optional clock.
> 
> Best regards,
> Krzysztof
>