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

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Message-ID: <7ae7f6a1-0ee1-4d56-b1d0-f038a7d22b4c@ti.com>
Date: Wed, 4 Feb 2026 20:03:39 -0600
From: Judith Mendez <jm@...com>
To: Markus Schneider-Pargmann <msp@...libre.com>, Alexander Sverdlin
	<alexander.sverdlin@...il.com>
CC: 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 Markus, Alexander,

On 2/3/26 4:35 AM, Markus Schneider-Pargmann wrote:
> Hi Judith,
> 
> On Wed Jan 14, 2026 at 11:04 PM CET, Judith Mendez wrote:
>> Hi Markus,
>>
>> On 1/14/26 3:16 AM, Markus Schneider-Pargmann wrote:
>>> Hi Judith,
>>>
>>> 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.

~ Judith