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

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Message-ID: <17a9ee62-8185-4833-acfc-1639fd17efc5@kernel.org>
Date: Wed, 21 May 2025 15:30:50 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: David Lechner <dlechner@...libre.com>
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 21/05/2025 15:23, David Lechner wrote:
> 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.

I do not see this needed at all. That's already handled by old code. You
only need to take new optional, second clock - axi clk. You take it by
index.

Best regards,
Krzysztof