[PATCH] mmc: Add power stabilization delay in mmc_power_on()

[Peng Fan]

> Subject: [PATCH] mmc: Add power stabilization delay in
> mmc_power_on()
> 
> From: Luke Wang <ziniu.wang_1 at nxp.com>
> 
> After enabling vmmc supply, add 10ms delay to allow voltage to
> stabilize before SD initialization starts. Without this delay, some SD
> cards fail to initialize because the initial clock cycles are sent while
> power is still ramping up.

There was an patch to add 2ms delay that missed in my mailbox and
I plan to pick it up.

https://lore.kernel.org/all/20251031145951.535376-1-c.stoidner@phytec.de/

That patch is for 1ms delay per spec requirement.

But here you added 10ms for power up ramp time, this should really
be in board off-on-delay-us because this is board specific stuff.

Adding 10ms here for all will enlarge boot time, I think this is
not good.

Thanks,
Peng.

> 
> Signed-off-by: Luke Wang <ziniu.wang_1 at nxp.com>
> ---
>  drivers/mmc/mmc.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c index
> bf82c515600..97037722fe1 100644
> --- a/drivers/mmc/mmc.c
> +++ b/drivers/mmc/mmc.c
> @@ -2878,6 +2878,12 @@ static int mmc_power_on(struct mmc
> *mmc)
>  			printf("Error enabling VMMC supply : %d\n",
> ret);
>  			return ret;
>  		}
> +
> +		/*
> +		 * Wait for power supply to stabilize before sending
> +		 * initial clock cycle.
> +		 */
> +		mdelay(10);
>  	}
> 
>  	if (mmc->vqmmc_supply) {
> --
> 2.34.1