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[MMC] Explain the internals of mmc_power_up()

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It seems that people get confused about what is happening in
mmc_power_up().  Add a comment to make it clear why we have
a two stage process.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Russell King 2005-12-14 14:57:35 +00:00 committed by Russell King
parent cd6104572b
commit 45f8245b97
1 changed files with 9 additions and 1 deletions
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10
drivers/mmc/mmc.c
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@ -679,7 +679,15 @@ static void mmc_idle_cards(struct mmc_host *host)
} }
/* /*
* Apply power to the MMC stack. * Apply power to the MMC stack. This is a two-stage process.
* First, we enable power to the card without the clock running.
* We then wait a bit for the power to stabilise. Finally,
* enable the bus drivers and clock to the card.
*
* We must _NOT_ enable the clock prior to power stablising.
*
* If a host does all the power sequencing itself, ignore the
* initial MMC_POWER_UP stage.
*/ */
static void mmc_power_up(struct mmc_host *host) static void mmc_power_up(struct mmc_host *host)
{ {