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mmc: Fix missing 1 ms delay after mmc power up

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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@phytec.de>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
This commit is contained in:
Christoph Stoidner
2025-10-31 15:59:51 +01:00
committed by Peng Fan
parent 141be72e2a
commit 21cdfd1992
1 changed files with 10 additions and 3 deletions
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13
drivers/mmc/mmc.c
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@@ -2933,11 +2933,18 @@ 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)