linux-kernel - Re: [PATCH v1] regulator: Don't error out fixed regulator in regulator_sync

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Date:   Thu, 21 Oct 2021 16:55:17 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Thierry Reding <treding@...dia.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH v1] regulator: Don't error out fixed regulator in
 regulator_sync_voltage()

21.10.2021 16:46, Dmitry Osipenko пишет:
> 21.10.2021 16:12, Mark Brown пишет:
>> On Thu, Oct 21, 2021 at 02:07:07PM +0300, Dmitry Osipenko wrote:
>>
>>> Fixed regulator can't change voltage and regulator_sync_voltage() returns
>>> -EINVAL in this case. Make regulator_sync_voltage() to succeed for a fixed
>>> regulator.
>>
>>> +++ b/drivers/regulator/core.c
>>> @@ -4249,6 +4249,9 @@ int regulator_sync_voltage(struct regulator *regulator)
>>>  	struct regulator_voltage *voltage = &regulator->voltage[PM_SUSPEND_ON];
>>>  	int ret, min_uV, max_uV;
>>>  
>>> +	if (rdev->desc->fixed_uV && rdev->desc->n_voltages == 1)
>>> +		return 0;
>>> +
>>>  	regulator_lock(rdev);
>>
>> It's unclear why this is checking both fixed_uV and n_voltages.
> 
> It's unclear to me either. I borrowed this variant from the  preexisting
> code [1][2].
> 
> [1]
> https://elixir.bootlin.com/linux/v5.15-rc6/source/drivers/regulator/core.c#L3075
> 
> [2]
> https://elixir.bootlin.com/linux/v5.15-rc6/source/drivers/regulator/core.c#L4319

The alternative could be to check regulator's capabilities:

if (!regulator_ops_is_valid(rdev, REGULATOR_CHANGE_VOLTAGE))
	return 0;

This looks like a better variant, actually.

>>  TBH
>> this feels like a higher level issue - with normal voltage configuration
>> we would have noticed that our constraints prevent the voltage changing
>> and not go as far as trying to actually apply a new configuration.  I
>> would expect a similar thing to be happening here.
>>
> 
> This works for a normal regulator_set_voltage() because it checks
> whether current voltage equals to the requested and then succeeds [3].
> The higher level code relies on this behaviour of the regulator core, in
> particular OPP core won't work without it and that's why voltage changes
> work for a fixed regulator.
> 
> [3]
> https://elixir.bootlin.com/linux/v5.15-rc6/source/drivers/regulator/core.c#L3619
> 
> This doesn't work for the regulator_sync_voltage() because it uses a
> different code path and the whole point is to re-apply the current
> voltage. Hence the extra check is actually needed for the fixed
> regulators in order to be consistent with the behaviour of
> regulator_set_voltage().
>