mmc: increase power up delay

Increase delay for power up in order to support some slower boards.

Also add some comments about why the delays are there.

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

1 files changed, 9 insertions, 1 deletions

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 3bebd3b55dc..bffcaf8df35 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -460,12 +460,20 @@ static void mmc_power_up(struct mmc_host *host)
         host->ios.timing = MMC_TIMING_LEGACY;
         mmc_set_ios(host);
 
-        mmc_delay(1);
+        /*
+         * This delay should be sufficient to allow the power supply
+         * to reach the minimum voltage.
+         */
+        mmc_delay(2);
 
         host->ios.clock = host->f_min;
         host->ios.power_mode = MMC_POWER_ON;
         mmc_set_ios(host);
 
+        /*
+         * This delay must be at least 74 clock sizes, or 1 ms, or the
+         * time required to reach a stable voltage.
+         */
         mmc_delay(2);
 }