From 45f8245b972e360c19aec9032e2a2033b8ac3719 Mon Sep 17 00:00:00 2001 From: Russell King Date: Wed, 14 Dec 2005 14:57:35 +0000 Subject: [MMC] Explain the internals of mmc_power_up() 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 --- drivers/mmc/mmc.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) (limited to 'drivers/mmc') diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c index b586a83a9b4c..eb41391e06e9 100644 --- a/drivers/mmc/mmc.c +++ b/drivers/mmc/mmc.c @@ -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) { -- cgit v1.2.3-59-g8ed1b