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authorRussell King <rmk@dyn-67.arm.linux.org.uk>2005-12-14 14:57:35 +0000
committerRussell King <rmk+kernel@arm.linux.org.uk>2005-12-14 14:57:35 +0000
commit45f8245b972e360c19aec9032e2a2033b8ac3719 (patch)
treee271207855406f5fb117126efd23cada5122456c /drivers/mmc
parentcd6104572bca9e4afe0dcdb8ecd65ef90b01297b (diff)
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[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>
Diffstat (limited to 'drivers/mmc')
-rw-r--r--drivers/mmc/mmc.c10
1 files changed, 9 insertions, 1 deletions
diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index b586a83..eb41391 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)
{
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