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

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Message-ID: <5342A3F5.606@topic.nl>
Date:	Mon, 7 Apr 2014 15:11:17 +0200
From:	Mike Looijmans <mike.looijmans@...ic.nl>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Ben Dooks <ben.dooks@...ethink.co.uk>, <linux-mmc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <cjb@...top.org>,
	<gdjakov@...sol.com>
Subject: Re: [PATCH] sdhci: Forward EPROBE_DEFER on vmmc and vqmmc regulators

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.

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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