[PATCH] mmc: Fix missing 1 ms delay after mmc power up

[Christoph Stoidner]

mmc/sd specification requires a 1 ms delay (stable supply voltage)
after vdd was enabled and before issuing first command.

For most sdcard/soc combinations, the missing delay seems to be not a
problem because the processing time between enabling vdd and the first
command is often hundreds of microseconds or more. However, in our
specific case, some sdcards were not detected by u-boot:
* soc: NXP i.MX 93
* sdcards: SanDisk Ultra, 64GB micro SDXC 1,
           MediaRange, 8GB, SDHC
* measured time between vdd and first command: approx. 784us
* symptom: both sdcards did not respond at all to first commands,
           u-boot mmc subsystem ran into timeout and stops to
           initialize the cards

Signed-off-by: Christoph Stoidner <c.stoidner at phytec.de>
Cc: Peng Fan <peng.fan at nxp.com>
Cc: Jaehoon Chung <jh80.chung at samsung.com>
---
 drivers/mmc/mmc.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index ec61ed92e86..2093d169094 100644
--- a/drivers/mmc/mmc.c
+++ b/drivers/mmc/mmc.c
@@ -2878,11 +2878,18 @@ static int mmc_power_cycle(struct mmc *mmc)
 		return ret;
 
 	/*
-	 * SD spec recommends at least 1ms of delay. Let's wait for 2ms
-	 * to be on the safer side.
+	 * SD spec recommends at least 1ms of 'power on' delay.
+	 * Let's wait for 2ms to be on the safer side.
 	 */
 	udelay(2000);
-	return mmc_power_on(mmc);
+	ret = mmc_power_on(mmc);
+
+	/*
+	 * SD spec recommends at least 1ms of 'stable supply voltage' delay.
+	 * Let's wait for 2ms to be on the safer side.
+	 */
+	udelay(2000);
+	return ret;
 }
 
 int mmc_get_op_cond(struct mmc *mmc, bool quiet)
-- 
2.43.0