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Date: Fri, 21 Nov 2014 13:06:18 +0100
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Subject: Re: [PATCH] mmc: dw_mmc: try pick the exact same voltage as vmmc for vqmmc
From: Ulf Hansson <ulf.hansson@linaro.org>
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Sender: linux-kernel-owner@vger.kernel.org

[...]

> 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
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