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

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Message-ID: <14a80484-5cfa-49bb-9608-12f25a113b23@baylibre.com>
Date: Wed, 21 May 2025 09:12:05 -0500
From: David Lechner <dlechner@...libre.com>
To: Uwe Kleine-König <ukleinek@...nel.org>
Cc: Michael Hennerich <michael.hennerich@...log.com>,
 Nuno Sá <nuno.sa@...log.com>,
 Trevor Gamblin <tgamblin@...libre.com>, 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 8:54 AM, Uwe Kleine-König wrote:
> Hello David,
> 
> On Wed, May 21, 2025 at 08:19:51AM -0500, David Lechner wrote:
>> On 5/21/25 4:22 AM, Uwe Kleine-König wrote:
>>> Can you achieve the same effect with the (IMHO slightly nicer but
>>> hand-crafted) following patch:
>>>
>>>  	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");
>>> +	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_optional(dev, "ext");
>>> +	if (IS_ERR(clk))
>>> +		return dev_err_probe(dev, PTR_ERR(clk), "failed to get ext clock\n");
>>> +	}
>>
>> The trouble with this is that it would not work with existing .dtbs
>> that don't have clock-names set. I think it would need to be more like this:
>>
>>
>> 	axi_clk = devm_clk_get_enabled(dev, NULL);
>> 	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_optional(dev, "ext");
>> 	if (IS_ERR(clk))
>> 		return dev_err_probe(dev, PTR_ERR(clk), "failed to get ext clock\n");
>>
>> 	if (!clk)
>> 		clk = axi_clk
>>
> 
> If there are no clock-names, the parameter is ignored. (I didn't test,
> only quickly checked the code.) So passing "axi" instead of NULL should
> work and yield a more robust solution.
> 
> Best regards
> Uwe


I didn't know that. So with your suggestion, I guess we would get/enable
the same clock twice. I guess that doesn't hurt anything. I will try it.