From mboxrd@z Thu Jan  1 00:00:00 1970
From: ulf.hansson@linaro.org (Ulf Hansson)
Date: Fri, 21 Nov 2014 13:06:18 +0100
Subject: [PATCH] mmc: dw_mmc: try pick the exact same voltage as vmmc for
 vqmmc
In-Reply-To: <5464152E.7040209@rock-chips.com>
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 <5464152E.7040209@rock-chips.com>
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To: linux-arm-kernel@lists.infradead.org
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[...]

> 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.

> and card can be identified. But if UHS card is pulgged in first, the vqmmc will be down to 1.8v.
>
> when sd2.0 card is pulgged in, mmc core will call dw_mci_switch_voltage to change vqmmc to 3.3v
> (MMC_SINGLE_VOTAGE_330). So vqmmc will be set 2.7v, if we request 2.7-3.6v.
>
> But vmmc is always 3.3v,becuase it be set min_volt = max_volt = 3.3v in dt tables.
>
> So the result:
> vmmc = 3.3v and vqmmc = 2.7v, and sd2.0 card is failed to identify in my test.

Hmm. I wonder why it works the first time? Could it be that your
regulator have voltage ramp up time that isn't properly considered?

Kind regards
Uffe