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>

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 3bebd3b55dc59af53545c9a42d877e8229ae0642..bffcaf8df35228749213347025346af4f52ca0b2 100644 (file)
--- 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);
 }