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

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Date:	Mon, 7 Apr 2014 14:32:20 +0200
From:	Mike Looijmans <mike.looijmans@...ic.nl>
To:	Arnd Bergmann <arnd@...db.de>,
	Ben Dooks <ben.dooks@...ethink.co.uk>
CC:	<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 02:25 PM, Arnd Bergmann wrote:
> On Monday 07 April 2014 13:18:54 Ben Dooks wrote:
>> On 07/04/14 13:16, Ben Dooks wrote:
>>> On 07/04/14 13:09, Mike Looijmans wrote:
>>>> On 04/07/2014 10:11 AM, Arnd Bergmann wrote:
>>>>> On Monday 07 April 2014 08:38:28 Mike Looijmans wrote:
>>>>>> index 34aef81..43b90c1 100644
>>>>>> --- a/drivers/mmc/host/sdhci.c
>>>>>> +++ b/drivers/mmc/host/sdhci.c
>>>>>> @@ -2972,6 +2972,8 @@ int sdhci_add_host(struct sdhci_host *host)
>>>>>>           host->vqmmc = regulator_get_optional(mmc_dev(mmc), "vqmmc");
>>>>>>           if (IS_ERR_OR_NULL(host->vqmmc)) {
>>>>>>                   if (PTR_ERR(host->vqmmc) < 0) {
>>>>>> +                       if (PTR_ERR(host->vqmmc) == -EPROBE_DEFER)
>>>>>> +                               return -EPROBE_DEFER;
>>>>>>                           pr_info("%s: no vqmmc regulator found\n",
>>>>>>                                   mmc_hostname(mmc));
>>>>>>                           host->vqmmc = NULL;
>>>>>> @@ -3048,8 +3050,10 @@ int sdhci_add_host(struct sdhci_host *host)
>>>>>>           host->vmmc = regulator_get_optional(mmc_dev(mmc), "vmmc");
>>>>>>           if (IS_ERR_OR_NULL(host->vmmc)) {
>>>>>>                   if (PTR_ERR(host->vmmc) < 0) {
>>>>>> -                       pr_info("%s: no vmmc regulator found\n",
>>>>>> -                               mmc_hostname(mmc));
>>>>>> +                       if (PTR_ERR(host->vmmc) == -EPROBE_DEFER)
>>>>>> +                               return -EPROBE_DEFER;
>>>>>> +                       pr_info("%s: no vmmc regulator found (%d)\n",
>>>>>> +                               mmc_hostname(mmc),
>>>>>> PTR_ERR(host->vmmc));
>>>>>>                           host->vmmc = NULL;
>>>>>>                   }
>>>>>
>>>>> Please change the code to not use IS_ERR_OR_NULL() instead, getting
>>>>> a NULL return value from regulator_get_optional() should not be
>>>>> considered a bug, while getting an error return should always
>>>>> cause the probe function to fail.
>>>
>>> Surely it needs to be changed to IS_ERR(), nor IS_ERR_OR_NULL()?
>>
>>
>> And by that, I mean the use of "PTR_ERR(host->vmmc) < 0" to be
>> changed to IS_ERR(), which I think Arnd was originally complaining
>> about.
>
> I mean something like
>
> 	host->vqmmc = regulator_get_optional(mmc_dev(mmc), "vqmmc");
>
> 	if (IS_ERR(host->vqmmc)) {
> 		if (PTR_ERR(host->vqmmc) != -EPROBE_DEFER)
> 			complain(); /* only print a message if we won't retry */
> 		return ERR_PTR(host->vqmmc); /* never ignore an error */
> 	}
> 	/* silently continue if no regulator is defined */
>
> regulator_get_optional() means we can continue if it's not there, but
> we should not continue if there is a regulator that we fail to use
> for some reason.
>
> As has been found a number of times, any use of IS_ERR_OR_NULL()
> means that the person responsible for the code is confused about
> what the API is supposed to be.

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...

Mike.



Met vriendelijke groet / kind regards,

Mike Looijmans

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