From 45f8245b972e360c19aec9032e2a2033b8ac3719 Mon Sep 17 00:00:00 2001
From: Russell King <rmk@dyn-67.arm.linux.org.uk>
Date: Wed, 14 Dec 2005 14:57:35 +0000
Subject: [PATCH] [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 <rmk+kernel@arm.linux.org.uk>
---
drivers/mmc/mmc.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
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)
{