linux-kernel - Re: [PATCH] arm64: dts: ti: k3-am62a7-sk: Disable mmc Schmitt Trigger

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Message-ID: <fcfcd3fb-2eac-4865-98f3-ef2ae24381bb@ti.com>
Date: Thu, 5 Feb 2026 11:07:19 -0600
From: Judith Mendez <jm@...com>
To: Francesco Dolcini <francesco@...cini.it>, Vitor Soares <ivitro@...il.com>
CC: Markus Schneider-Pargmann <msp@...libre.com>, Alexander Sverdlin
	<alexander.sverdlin@...il.com>, Vishal Mahaveer <vishalm@...com>, "Kevin
 Hilman" <khilman@...libre.com>, Dhruva Gole <d-gole@...com>, Sebin Francis
	<sebin.francis@...com>, Kendall Willis <k-willis@...com>, Akashdeep Kaur
	<a-kaur@...com>, <linux-arm-kernel@...ts.infradead.org>,
	<devicetree@...r.kernel.org>, Conor Dooley <conor+dt@...nel.org>, "Krzysztof
 Kozlowski" <krzk+dt@...nel.org>, Rob Herring <robh@...nel.org>,
	<linux-kernel@...r.kernel.org>, Nishanth Menon <nm@...com>, "Vignesh
 Raghavendra" <vigneshr@...com>, Tero Kristo <kristo@...nel.org>
Subject: Re: [PATCH] arm64: dts: ti: k3-am62a7-sk: Disable mmc Schmitt Trigger

Hi Fransesco,

On 2/5/26 1:24 AM, Francesco Dolcini wrote:
> Hello Judith,
> 
> On Wed, Feb 04, 2026 at 08:03:39PM -0600, Judith Mendez wrote:
>> On 2/3/26 4:35 AM, Markus Schneider-Pargmann wrote:
>>> On Wed Jan 14, 2026 at 11:04 PM CET, Judith Mendez wrote:
>>>> On 1/14/26 3:16 AM, Markus Schneider-Pargmann wrote:
>>>>> On Tue Jan 13, 2026 at 1:29 AM CET, Judith Mendez wrote:
>>>>>> On 1/6/26 10:22 AM, Markus Schneider-Pargmann (TI.com) wrote:
>>>>>>> Remove Schmitt Trigger from mmc pins. With Schmitt Trigger enabled
>>>>>>> u-boot SPL is not able to read u-boot from mmc:
>>>>>>>
>>>>>>>         Trying to boot from MMC2
>>>>>>>         Error reading cluster
>>>>>>>         spl_load_image_fat: error reading image u-boot.img, err - -22
>>>>>>>         Error: -22
>>>>>>>         SPL: Unsupported Boot Device!
>>>>>>>         SPL: failed to boot from all boot devices
>>>>>>>         ### ERROR ### Please RESET the board ###
>>>>>>>
>>>>>>> I bisected this issue between u-boot v2025.10 and v2026.01 and found the
>>>>>>> devicetree merge to be the problem. At a closer look I found the
>>>>>>> k3-pinctrl.h changes. Disabling the Schmitt Trigger fixes the u-boot SPL
>>>>>>> failure to read from mmc.
>>>>>>
>>>>>> I have tested 4 AM62A SK boards and I cannot replicate the issue
>>>>>> you are seeing. I do not see an issue with Schmitt Trigger in U-boot
>>>>>> nor Linux /:
>>>>>
>>>>> Thanks for testing.
>>>>>
>>>>>> Can you please run a quick tap sweep on MMC1 and MMC0 interfaces like
>>>>>> so? https://gist.github.com/jmenti/f4a73a8323e44bf717c6d2c528c499ca
>>>>>>
>>>>>> This will give me an idea if whether we should be talking about
>>>>>> revisiting characterization with ST_ENA=1.
>>>>>
>>>>> The patch was a bit broken, but I think I managed to apply it to
>>>>> v2026.01 as it was supposed to be. (master currently doesn't boot even
>>>>> SPL, I don't have time right now to debug that).
>>>>
>>>> as Nishanth, mentioned, master is missing two patches [0][1]
>>>>
>>>>>
>>>>> I attached the boot log. It does boot with your patch. Also can this be
>>>>> an issue with different SD cards?
>>>>
>>>> Something does not quite add up,
>>>>
>>>> Can you try the following 2 commands?
>>>>
>>>> # mmc dev 1
>>>> # md.w 0xfa0810c
>>>
>>> Finally here is the output from boot and executing these commands. I am
>>> now on v2026.04-rc1 with your sweep patch.
>>
>> Thanks for sending over the tap sweep. I compiled a comparison table
>> here to show a bit of data for the u-boot tuning step:
>> https://gist.github.com/jmenti/5d42f1e43fb357083eaa813cfee484a8
>>
>> Based on the data I can conclude the following:
>> 1. you seem to have more errors than I do
>> 2. there seems to be an issue with the chosen final tap setting
>> 3. the chosen final tap setting should still have worked for you
>> but did not.
>>
>> For #2, something in the tuning results seems off so let me investigate
>> this on my end and Ill get back.
>> For #3, will have to discuss this internally & test a couple more things,
>> then come back with more information.
>>
>> Meanwhile, I am interested to see what are the tap sweep results for the
>> failing Verdin board, if those can be sent as well, that would be great
>> info.
> 
> Verdin is now booting fine. The boot failure was related to other U-Boot
> bugs (as Nishanth mentioned) that are now fixed.

Good to know, that isolates the issue to only one board.

Thanks.

~ Judith