Re: [PATCH] mmc: dts: am654: Add 650ms power off delay for proper MMC power cycle

[Nishanth Menon <nm@ti.com>]

On 12:29-20260908, Judith Mendez wrote:
> Hi Nishanth,
> 
> On 9/8/26 12:16, Nishanth Menon wrote:
> > On 12:06-20260908, Judith Mendez wrote:
> > > The AM65x EVM MMC1 VDD rail discharges slowly through RC circuit.
> > > SD spec (section 6.4.1.3) requires VDD < 0.5V for minimum 1ms during
> > > power cycle. Measured discharge time on this board is ~632.97ms to
> > > reach < 0.5V threshold.
> > > 
> > > During boot, MMC power cycles between boot stages. Without power off
> > > delay, VDD doesn't fully discharge. Card retains 1.8V signaling state
> > > from previous stages. When U-Boot initializes, card no longer asserts
> > > S18A in ACMD41 response (already switched to 1.8V). Host misinterprets
> > > card state and forces 1.8V anyway, falling into a bad state and causing
> > > a boot failure.
> > > 
> > > Add power-off-delay-us = 650000 (650ms) to ensure proper VDD discharge
> > > during power cycles, allowing card to fully reset state between boot
> > > stages.
> > > 
> > > Signed-off-by: Judith Mendez <jm@ti.com>
> > 
> > Fixes ?
> 
> Fix is really for u-boot, don't think I can point to a u-boot
> commit here can I?

You'd face the same problem if you are starting from a different boot
media and then enable MMC in linux kernel, right? what was described in
the patch sounds like a discharge latency of the evm. This was missed in
the original commit?

-- 
Regards,
Nishanth Menon
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