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| author |   Russell King <rmk@dyn-67.arm.linux.org.uk> | 2005-12-14 14:57:35 +0000 |
|---|---|---|
| committer |   Russell King <rmk+kernel@arm.linux.org.uk> | 2005-12-14 14:57:35 +0000 |
| commit | 45f8245b972e360c19aec9032e2a2033b8ac3719 (patch) | |
| tree | e271207855406f5fb117126efd23cada5122456c /drivers/mmc | |
| parent | [PATCH] hid-core: Zero-pad truncated reports (diff) | |
| download | linux-dev-45f8245b972e360c19aec9032e2a2033b8ac3719.tar.xz linux-dev-45f8245b972e360c19aec9032e2a2033b8ac3719.zip | |
[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.c | 10 |
1 files changed, 9 insertions, 1 deletions
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) { |