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

[Peng Fan]

> Subject: Re: AW: [PATCH] mmc: Fix missing 1 ms delay after mmc
> power up
> 
> Hi Peng,
> 
> On Di, 2025-11-18 at 12:56 +0800, Peng Fan wrote:
> > 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.
> 
> you mean we should introduce the DTS property
> post_power_delay_ms for mmc and then use it in our platform's DTS?
> 
> But a DTS property is actually what I want to avoid, because that delay
> is nothing platform-specific and should be solved all for one in the
> mmc subsystem drivers/mmc/mmc.c itself.
> 
> What's the reason why you prefer a DTS property?

You message seems breaks the mail thread. So my script not
able to retrieve the message thread from patchwork.

I just don't like to add delays. Reading the spec again,
I am fine with your changes. 

Thanks,
Peng.

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