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

[Judith Mendez]

Hi Nishanth,

On 9/9/26 05:36, Nishanth Menon wrote:
> 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@xxxxxx>
> > > > >
> > > > > 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@xxxxxx/
> > [1] https://lore.kernel.org/linux-mmc/20260806162202.657512-1-jm@xxxxxx/
>
> 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

Ok, will fixup coverletter and subject for v2.

Thanks.
~ Judith