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

[Nishanth Menon]

On 13:13-20260908, Judith Mendez wrote:
> Hi Nishanth,
> 
> On 9/8/26 12:49, Nishanth Menon wrote:
> > 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 at 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?
> > 
> 
> Not exactly. The failure is only seen at u-boot specifically with
> SD card boot. Very specifically due to the MMC driver in u-boot and
> commit [0] which is not reverted since it is technically correct.
> The commit just happened to expose our EVM's issue first. According to
> the discussion, mirror Linux patch may be coming soon, which we are
> now prepared for with this patch and [1].
> 
> [0]
> https://lore.kernel.org/u-boot/d17a810c-e2db-4a24-a37d-2d7e02466ce9@ti.com/
> [1] https://lore.kernel.org/linux-mmc/20260806162202.657512-1-jm@ti.com/

This context is useful in diffstat. I see the driver fix in kernel which
can use this property not present in previous kernels, hence no fixes.

That said, please fix $subject for v2 and repost. I suggest:
arm64: dts: ti: k3-am654-base-board: Add power off delay for proper MMC power cycle

-- 
Regards,
Nishanth Menon
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