linux-kernel - Re: [PATCH v6 4/4] x86/sev: register tpm-svsm platform device

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Message-ID: <20250409183803.GKZ_a-i3YZM4WfpkeU@fat_crate.local>
Date: Wed, 9 Apr 2025 20:38:03 +0200
From: Borislav Petkov <bp@...en8.de>
To: James Bottomley <James.Bottomley@...senpartnership.com>
Cc: Stefano Garzarella <sgarzare@...hat.com>,
	Jarkko Sakkinen <jarkko@...nel.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>,
	"H. Peter Anvin" <hpa@...or.com>, linux-coco@...ts.linux.dev,
	linux-integrity@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	x86@...nel.org, Tom Lendacky <thomas.lendacky@....com>,
	Joerg Roedel <jroedel@...e.de>,
	Dionna Glaze <dionnaglaze@...gle.com>,
	Claudio Carvalho <cclaudio@...ux.ibm.com>,
	linux-kernel@...r.kernel.org, Dov Murik <dovmurik@...ux.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v6 4/4] x86/sev: register tpm-svsm platform device

On Wed, Apr 09, 2025 at 08:22:37AM -0400, James Bottomley wrote:
> Because of the way driver and device matching works in Linux.  We have
> to have a struct device because that sits at the he heart of the TPM
> driver binding.  If we have a struct device, it has to sit on a bus
> (because that's the Linux design) and if we don't have a bus then we
> have to use a platform device

Thanks for elaborating!

> (or, now, we could use a struct device on the faux bus).  Busses can be
> either physical (PCI, GSC, ...) and abstract (virtio, xen, scsi, ...), so
> it's not impossible, if the SVSM has more than one device, that it should
> have it's own SVSM bus which we could then act a bit like the virtio bus and
> the SVSM vTPM struct device could sit on this 

I guess we should keep this in mind. Depending on what else needs to talk to
the SVSM in the future...

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette