linux-kernel - Re: [PATCH v8 1/2] pwm: meson: Add support for Amlogic S4 PWM

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Message-ID: <1jbk44htqr.fsf@starbuckisacylon.baylibre.com>
Date: Fri, 14 Jun 2024 09:24:28 +0200
From: Jerome Brunet <jbrunet@...libre.com>
To: Uwe Kleine-König <u.kleine-koenig@...libre.com>
Cc: Kelvin Zhang via B4 Relay <devnull+kelvin.zhang.amlogic.com@...nel.org>,
  Neil Armstrong <neil.armstrong@...aro.org>,  Kevin Hilman
 <khilman@...libre.com>,  Martin Blumenstingl
 <martin.blumenstingl@...glemail.com>,  Rob Herring <robh@...nel.org>,
  Krzysztof Kozlowski <krzk+dt@...nel.org>,  Conor Dooley
 <conor+dt@...nel.org>,  kelvin.zhang@...ogic.com,
  linux-pwm@...r.kernel.org,  linux-arm-kernel@...ts.infradead.org,
  linux-amlogic@...ts.infradead.org,  linux-kernel@...r.kernel.org,
  devicetree@...r.kernel.org,  Junyi Zhao <junyi.zhao@...ogic.com>
Subject: Re: [PATCH v8 1/2] pwm: meson: Add support for Amlogic S4 PWM

On Thu 13 Jun 2024 at 22:46, Uwe Kleine-König <u.kleine-koenig@...libre.com> wrote:

> Hello,
>
> On Thu, Jun 13, 2024 at 05:54:31PM +0200, Jerome Brunet wrote:
>> > +	for (i = 0; i < MESON_NUM_PWMS; i++) {
>> > +		meson->channels[i].clk = of_clk_get(np, i);
>> > +		if (IS_ERR(meson->channels[i].clk))
>> > +			return dev_err_probe(dev,
>> > +					     PTR_ERR(meson->channels[i].clk),
>> > +					     "Failed to get clk\n");
>> 
>> here it is ok but ..
>> 
>> > +
>> > +		ret = devm_add_action_or_reset(dev, meson_pwm_s4_put_clk,
>> > +					       meson->channels[i].clk);
>> > +		if (ret)
>> > +			return dev_err_probe(dev, ret,
>> > +					     "Failed to add clk_put action\n");
>> 
>> ... here, devm_add_action_or_reset cannot defer, so dev_err_probe is not useful.
>> dev_err() if you must print something. Just "return ret;" would be fine
>> by me
>
> I don't agree. dev_err_probe() has several purposes. Only one of them is
> handling -EPROBE_DEFER. See also commit
> 532888a59505da2a3fbb4abac6adad381cedb374.

I was stuck on the -EPROBE_DEFER usage. Thanks for the heads up

>
> So yes, please use dev_err_probe() also to handle
> devm_add_action_or_reset().

My point here is also that devm_add_action_or_reset() can only fail on
memory allocation, like (devm_)kzalloc. Looking around the kernel, we
tend to not add messages for that and just return the error code,
presumably because those same 'out of memory' messages would proliferate
everywhere.

>
> Best regards
> Uwe

-- 
Jerome