linux-kernel - Re: tpm: SLM9670 does not work on T1023

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Message-ID: <aMLh7MCsPNwOqTsG@FUE-ALEWI-WINX>
Date: Thu, 11 Sep 2025 16:51:24 +0200
From: Alexander Wilhelm <alexander.wilhelm@...termo.com>
To: Mark Brown <broonie@...nel.org>
Cc: Peter Huewe <peterhuewe@....de>, Jarkko Sakkinen <jarkko@...nel.org>,
        linux-integrity@...r.kernel.org, linux-spi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: tpm: SLM9670 does not work on T1023

On Thu, Sep 11, 2025 at 03:26:38PM +0100, Mark Brown wrote:
> On Thu, Sep 11, 2025 at 03:52:33PM +0200, Alexander Wilhelm wrote:
> 
> > However, the driver reads an incorrect vendor ID (0x1000000) and hangs during
> > the startup sequence. A logic analyzer shows that the chip select line goes high
> > immediately after transmitting 4 bytes, which, according to various forum
> > discussions, does not comply with the TPM specification. Unfortunately, I
> > haven't found a definitive solution to this issue.
> 
> That sounds like the controller is configured in word mode and is
> bouncing chip select after every word it sends.  The Freescale
> controllers are fond of implementing and using that, no idea about this
> specific one.  I see there's some non-standard DT properties it has
> which look like they're related to chip select modes but no idea what
> they do.

Which DT properties are you referring to? I’ve only used the default ones
provided by the QorIQ DTS files in the kernel.

> > Could this be a bug in the `spi-fsl-espi` driver, or is it possibly a hardware
> > limitation of the T1023? I've come across some suggestions that involve using a
> > GPIO as an alternative chip select instead of the one provided by the SPI
> > controller. Can anyone confirm whether this workaround is viable? I’d prefer to
> > avoid a PCB redesign unless it's absolutely necessary.
> 
> Can you not pinmux the signal from the SoC to a GPIO instead of the SPI
> controller?  It's fairly common to do that since controllers often have
> regrettably limited or unhelpful chip select features so GPIOs are often
> the better choice.  The controller does what it likes with the chip
> select signal but it's not actually connected to anything and we do
> everything in software.

The problem here is that RCW allows either both enabled SPI + CS or disabled SPI
and CS-pins set to GPIO. Furthermore it is unfortunatelly connected, so I cannot
simple cut the path on PCB and need a more complicated re-design of it.

The issue here is that the RCW configuration either enables both SPI and CS
together, or disables SPI and sets the CS pins to GPIO. Unfortunately, the PCB
traces are laid out in a way that prevents me from simply cutting the
connection. A more complex redesign would be required.

> I'd recommend contacting whoever looks after the relevant controller
> driver, though it looks rather abandoned TBH.

Hopefully, someone with experience in this kind of setup will respond via the
mailing list.


Best regards
Alexander Wilhelm