linux-kernel - Re: [PATCH] regulator: change stubbed devm_regulator_get

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Date: Tue, 23 Apr 2024 08:11:57 +0300
From: Matti Vaittinen <mazziesaccount@...il.com>
To: Guenter Roeck <linux@...ck-us.net>,
 Matti Vaittinen <matti.vaittinen@...rohmeurope.com>
Cc: Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>,
 linux-kernel@...r.kernel.org, Aleksander Mazur <deweloper@...pl>
Subject: Re: [PATCH] regulator: change stubbed devm_regulator_get_enable to
 return Ok

On 4/22/24 16:23, Guenter Roeck wrote:
> On 4/21/24 23:38, Matti Vaittinen wrote:
>> The devm_regulator_get_enable() should be a 'call and forget' API,
>> meaning, when it is used to enable the regulators, the API does not
>> provide a handle to do any further control of the regulators. It gives
>> no real benefit to return an error from the stub if CONFIG_REGULATOR is
>> not set.
>>
>> On the contrary, returning and error is causing problems to drivers when
>> hardware is such it works out just fine with no regulator control.
>> Returning an error forces drivers to specifically handle the case where
>> CONFIG_REGULATOR is not set, making the mere existence of the stub
>> questionalble. Furthermore, the stub of the regulator_enable() seems to
>> be returning Ok.
>>
> 
> Yes, that was the reason why the lm90 driver worked pripr to its conversion
> to use devm_regulator_get_enable() if CONFIG_REGULATOR=n.
> 
>> Change the stub implementation for the devm_regulator_get_enable() to
>> return Ok so drivers do not separately handle the case where the
>> CONFIG_REGULATOR is not set.
>>
>> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
>> Reported-by: Aleksander Mazur <deweloper@...pl>
>> Suggested-by: Guenter Roeck <linux@...ck-us.net>
>> Fixes: da279e6965b3 ("regulator: Add devm helpers for get and enable")
>>
>> ---
>> Please find the report by Aleksander from:
>> https://lore.kernel.org/all/20240420183427.0d3fda27@mocarz/
>>
>> This patch has not received testing. It'd be great to hear if this
>> solves the issue.
>>
>> I see the regulator_get_exclusive() and devm_regulator_get_optional()
>> returning errors. I thus leave the
>> devm_regulator_get_enable_[optional/exclusive]() to do the same while
>> wondering if this is the right thing to do, and why...
>>
> 
> At least one of the callers of devm_regulator_get_enable (exc3000) 
> checks for
> -ENODEV and ignores it. I assume we'll see more of those unless this patch
> is accepted. Many of the callers of devm_regulator_get_enable_optional()
> explicitly check for -ENODEV and ignore it. Others fail if 
> CONFIG_REGULATOR=n.
> My plan for affected hwmon drivers is (was ?) to check for -ENODEV and 
> ignore
> it to match other drivers.

I'd rather fixed the stub than the callers. I suspect same goes with 
other subsystems.

> Returning ERR_PTR(-ENODEV) for [devm_]regulator_get() made sense because
> the returned regulator pointer was often used to obtain a voltage or to
> do other regulator operations. I don't really see the point of returning
> -ENODEV for the _enable APIs if regulator support is disabled.

I agree. I'll send another one for the 
devm_regulator_get_enable_[optional/exclusive]() if Mark accepts this one.

Thanks for the heads up!

Yours,
	-- Matti

-- 
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

~~ When things go utterly wrong vim users can always type :help! ~~