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

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Message-ID: <99c6295c-9ed8-4611-a3db-ad57a33f4f38@baylibre.com>
Date: Wed, 21 May 2025 08:53:43 -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 8:30 AM, Krzysztof Kozlowski wrote:
> 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.

Except that it is the "ext" clock that is supposed to be optional and
the "axi" clock is supposed to be required.

> 
> Best regards,
> Krzysztof