linux-kernel - Re: [PATCH] sdhci: Forward EPROBE_DEFER on vmmc and vqmmc regulators

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Message-ID: <CAL1qeaET+cy19EtB_TbtQ40Lb9r9hrO4H5vjG5YmCTpYoOmcog@mail.gmail.com>
Date:	Wed, 16 Apr 2014 13:15:53 -0700
From:	Andrew Bresticker <abrestic@...omium.org>
To:	Mike Looijmans <mike.looijmans@...ic.nl>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Ben Dooks <ben.dooks@...ethink.co.uk>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	cjb@...top.org, gdjakov@...sol.com,
	"broonie@...nel.org" <broonie@...nel.org>
Subject: Re: [PATCH] sdhci: Forward EPROBE_DEFER on vmmc and vqmmc regulators

Hi Mike,

On Mon, Apr 7, 2014 at 6:11 AM, Mike Looijmans <mike.looijmans@...ic.nl> wrote:
> On 04/07/2014 02:51 PM, Arnd Bergmann wrote:
>>
>> On Monday 07 April 2014 14:32:20 Mike Looijmans wrote:
>>>
>>> On 04/07/2014 02:25 PM, Arnd Bergmann wrote:
>>>
>>> Judging from the kernel output, regulator_get_optional returns -ENODEV if
>>> the
>>> supply wasn't found.
>>>
>>> Maybe the API is confusing (or wrong?) here.
>>>
>>> If you change the code as per your suggestion, the SD will not work
>>> unless you
>>> explicitly assign supplies. And judging from what I've seen so far, I am
>>> the
>>> first to have ever attached a power supply to this controller...
>>
>>
>> It's certainly not very "optional" if it returns an error here.
>>
>> You could try to special-case the "-ENODEV" return here, but I think it
>> would be better to change the regulator interface to be less confusing.
>>
>
> Judging from the code:
> http://lxr.free-electrons.com/source/drivers/regulator/core.c#L1476
>
> The behaviour is supposed to be something like "regulator_get_optional" will
> return an error if the supply wasn't found, but "regulator_get" will create
> a dummy supply for you instead of returning an error code.
>
> So "regulator_get_optional" means: "I handle my own problems, just gimme the
> bad news". But "regulator_get" appears to imply: "I will shoot the
> messenger, so do whatever you can to get me something to say 'enable' to".
>
> In this case, the IS_NULL part is wrong indeed, it will never return NULL.

Not true.  If !CONFIG_REGULATOR, regulator_get() and co. will return
NULL.  Normally it is ok to ignore this case, but the sdhci driver
will call regulator_is_supported_voltage() on vqmmc to determine
whether 1.8V signalling is supported.  With !CONFIG_REGULATOR,
regulator_is_supported_voltage() will always return false, causing the
sdhci driver to disable all UHS modes.  So we still need to handle the
NULL (!CONFIG_REGULATOR) case.  One possibility is to guard the
voltage check with #ifdef CONFIG_REGULATOR, as is done later with
vmmc.

BTW, I was working on a similar patch at:
https://patchwork.kernel.org/patch/3988271/.

Thanks,
Andrew

>
> I still think it's unrelated to my patch and should be submitted separately.
>
>
> Mike.
>
>
> Met vriendelijke groet / kind regards,
>
> Mike Looijmans
>
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