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 <[email protected]>
Cc: Peng Fan <[email protected]>
Cc: Jaehoon Chung <[email protected]>
---
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
