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

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Date: Mon, 22 Apr 2024 06:23:40 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Matti Vaittinen <mazziesaccount@...il.com>,
 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 4/21/24 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.

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.

Anyway, for this patch:

Reviewed-by: Guenter Roeck <linux@...ck-us.net>

Thanks,
Guenter