linux-kernel - Re: Warnings for invalid VDD (sdhci-s3c)

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Date:	Thu, 24 Mar 2016 16:24:49 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	Jaehoon Chung <jh80.chung@...sung.com>
CC:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	<ludovic.desroches@...el.com>,
	"Ivan T. Ivanov" <ivan.ivanov@...aro.org>,
	<linux-mmc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-samsung-soc@...r.kernel.org>
Subject: Re: Warnings for invalid VDD (sdhci-s3c)

Hi,

On Thu, 24 Mar 2016 17:09:27 +0900 Jaehoon Chung wrote:

> Hi,
> 
> On 03/24/2016 04:58 PM, Jisheng Zhang wrote:
> > Hi,
> > 
> > On Thu, 24 Mar 2016 16:28:56 +0900 Krzysztof Kozlowski wrote:
> >   
> >> Hi,
> >>
> >> After 918f4cbd4340 ("mmc: sdhci: restore behavior when setting VDD via
> >> external regulator") On Trats2 board I see warnings for invalid VDD
> >> value (2.8V):
> >>
> >> [    3.119656] ------------[ cut here ]------------
> >> [    3.119666] WARNING: CPU: 3 PID: 90 at
> >> ../drivers/mmc/host/sdhci.c:1234 sdhci_do_set_ios+0x4cc/0x5e0
> >> [    3.119669] mmc0: Invalid vdd 0x10  
> > 
> > Per my understanding, the wrong vdd indicates a wrong ocr, what's the voltage of
> > this host's vmmc regulator?  
> 
> As i know, it's fixed-voltage with gpio on trats2. It's 2.8V.
> I didn't check this entirely..need to check ocr value.
> 

I may know the reason. the vmmc is 2.8v, then mmc_regulator_get_supply() convert
the value to a ocr as 0x10. The key here is that the 2.8v is invalid in SDHCI
case and isn't accepted by current sdhci driver.

I dunno the elegant solution to handle this case, let's wait for sdhci maintainers
idea.

Thanks,
Jisheng