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

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Message-ID: <20260205072439.GA4548@francesco-nb>
Date: Thu, 5 Feb 2026 08:24:39 +0100
From: Francesco Dolcini <francesco@...cini.it>
To: Judith Mendez <jm@...com>, 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

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.

Thanks
Francesco