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

[Judith Mendez <jm@ti.com>]

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@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
> 

Ok, will fixup coverletter and subject for v2.

Thanks.
~ Judith