Re: [PATCH] mmc: dw_mmc: try pick the exact same voltage as vmmc for vqmmc

From: Doug Anderson <dianders@chromium.org>
To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: "addy ke" <addy.ke@rock-chips.com>,
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Subject: Re: [PATCH] mmc: dw_mmc: try pick the exact same voltage as vmmc for vqmmc
Date: Fri, 21 Nov 2014 09:42:08 -0800	[thread overview]
Message-ID: <CAD=FV=Ve1TY4+8quq1=18A1YOFvOWuFGrBmHLwMCwdWBSqzxOw@mail.gmail.com> (raw)
In-Reply-To: <CAPDyKFrzGfDew0eLLEcA+_iS_mo-O2bFU58fjirfXXA8AJ9UYQ@mail.gmail.com>

Ulf,

On Fri, Nov 21, 2014 at 4:06 AM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> [...]
>
>> Sure
>> If the first card is sd2.0 since startup, dw_mci_switch_voltage will not be called,
>
> That can't be right. mmc_power_up() should trigger
> dw_mci_switch_voltage() to be invoked.

Hmmm, I think you're right.  Addy: can you double check if it's only
the 2nd card for you?  I was thinking that if a regulator is currently
3.3V and you request 2.7 - 3.3V the regulator framework will treat
that as a noop.  ...but that definitely doesn't appear to be the case.
When I boot up the first time even with no SD card plugged in, I see
this at bootup:

[    3.042234] vccio_sd: 1800 <--> 3300 mV at 3300 mV

...showing that it started at 3.3V.  Then I see:

$ grep "" /sys/class/regulator/regulator.16/{name,microvolts}
/sys/class/regulator/regulator.16/name:vccio_sd
/sys/class/regulator/regulator.16/microvolts:2700000

...so it is certainly getting changed even with no card plugged in.

BTW: I don't actually have one of these failing cards--all of mine
work.  Addy, do you know the make and model of the card you have that
fails?

-Doug