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

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Message-ID: <p3ejuwktdxcjwv43nnap5tin33ziimgxfan2xoghtaaubsxgy7@tjmwjpwy6yy5>
Date: Wed, 21 May 2025 15:54:17 +0200
From: Uwe Kleine-König <ukleinek@...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>, 
	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

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

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