From: Russell King <rmk@dyn-67.arm.linux.org.uk>
Date: Wed, 14 Dec 2005 14:57:35 +0000 (+0000)
Subject: [MMC] Explain the internals of mmc_power_up()
X-Git-Tag: v2.6.15-rc6~64^2
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=45f8245b972e360c19aec9032e2a2033b8ac3719;p=linux-2.6

[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>
---

diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index b586a83a9b..eb41391e06 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)
 {