linux-kernel - Re: [PATCH 2/2] dt-bindings: tpm: Add st,st33ktpm2xi2c to TCG TIS binding

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Date: Sat, 13 Apr 2024 12:51:15 +0200
From: Lukas Wunner <lukas@...ner.de>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: "M. Haener" <michael.haener@...mens.com>,
	linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
	Peter Huewe <peterhuewe@....de>,
	Jarkko Sakkinen <jarkko@...nel.org>, Jason Gunthorpe <jgg@...pe.ca>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Alexander Sverdlin <alexander.sverdlin@...mens.com>
Subject: Re: [PATCH 2/2] dt-bindings: tpm: Add st,st33ktpm2xi2c to TCG TIS
 binding

On Sat, Apr 13, 2024 at 12:43:38PM +0200, Krzysztof Kozlowski wrote:
> On 13/04/2024 12:34, Lukas Wunner wrote:
> > The other patch just adds an entry to of_tis_i2c_match[] in the driver,
> > pretty unspectacular:
> > 
> > https://lore.kernel.org/all/20240413071621.12509-2-michael.haener@siemens.com/
> 
> Then why is it needed?

The binding requires two entries in the compatible string used in the DT,
the chip name followed by the generic string:

        items:
          - enum:
              - infineon,slb9673
              - nuvoton,npct75x
          - const: tcg,tpm-tis-i2c

This allows us to deal with device-specific quirks, should they pop up
(e.g. special timing requirements, hardware bugs).  We don't know in
advance if they will be discovered, but if they are, it's cumbersome
to determine after the fact which products (and thus DTs) are affected.
So having the name of the actual chip used on the board has value.

Thanks,

Lukas