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

[Peng Fan <peng.fan@oss.nxp.com>]

On Mon, Nov 10, 2025 at 08:46:39PM +0000, Christoph Stoidner wrote:
>Hi Peng, thanks for your feedback.
>
>> Hi Christoph
>> 
>> Thanks for your patch.
>> 
>> > Subject: [PATCH] mmc: Fix missing 1 ms delay after mmc power up
>...
>> > +     udelay(2000);
>> 
>> Per spec,
>> From Figure 6-4: Power-up Diagram of Card
>> the 1ms is voltageSupply ramp up time, so I am thinking the fix
>> should be in your regulator side, saying startup-delay-us property
>> in your regulator node.
>
>True, this could also be handled via the regulator?s DTS properties, and
>some boards already do that. However, from my point of view, that?s not
>the right place for this particular delay.
>
>The SD specification distinguishes between two different delays
>(see Figure 6-5 ?Power-Up Diagram (Host)? in SD Spec 6.00, ?6.4.1):
>
>   1) "Power ramp up"
>   2) "Stable voltage delay"
>
>The first one (power ramp up) is regulator-specific and should indeed be
>covered by the regulator?s startup-delay-us property in the device tree.
>But this patch is about the second one - the "stable voltage delay".
>
>That delay is completely independent of any regulator/voltage-supply or
>board characteristics; it is a constant 1ms delay by the SD interface itself
>to ensure correct card initialization timing. 
>Decoupling it from the regulators would make board-code developers
>live easier, and can make U-Boot?s MMC initialization more robust across
>all boards.
>
>What do you think about that?

Sorry for late.
Thanks for explaining this, this is reasonable. I am thinking it might be better
if we add ios.post_power_delay_ms for your platform.

Regards
Peng

>
>Regards,
>Christoph
>
>> Thanks,
>> Peng.
>> 
>> > +     return ret;
>...