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

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Message-ID: <aMLUIVjHZ6CFvd33@fue-alewi-winx>
Date: Thu, 11 Sep 2025 15:52:33 +0200
From: Alexander Wilhelm <alexander.wilhelm@...termo.com>
To: Peter Huewe <peterhuewe@....de>, Jarkko Sakkinen <jarkko@...nel.org>,
        Mark Brown <broonie@...nel.org>
Cc: linux-integrity@...r.kernel.org, linux-spi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: tpm: SLM9670 does not work on T1023

Hello devs,

I'm trying to bring up the SLM9670 TPM 2.0 device connected via SPI on a QorIQ
T1023-based board. Pin control is fully configured through the RCW, so I haven't
added any additional properties in the device tree. The SPI controller accesses
the TPM using `#CS0`.

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.

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.

Best regards
Alexander Wilhelm