linux-kernel - Re: [RFC PATCH v2 3/6] tpm: add send_recv() ops in tpm_class

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Message-ID: <Z8sfiDEhsG6RATiQ@kernel.org>
Date: Fri, 7 Mar 2025 18:32:08 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: Jason Gunthorpe <jgg@...pe.ca>, Thomas Gleixner <tglx@...utronix.de>,
	Claudio Carvalho <cclaudio@...ux.ibm.com>,
	Peter Huewe <peterhuewe@....de>, x86@...nel.org,
	Dov Murik <dovmurik@...ux.ibm.com>, linux-coco@...ts.linux.dev,
	Dionna Glaze <dionnaglaze@...gle.com>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
	linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Tom Lendacky <thomas.lendacky@....com>,
	Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC PATCH v2 3/6] tpm: add send_recv() ops in tpm_class_ops

On Fri, Mar 07, 2025 at 04:37:12PM +0100, Stefano Garzarella wrote:
> On Thu, Mar 06, 2025 at 11:52:46PM +0200, Jarkko Sakkinen wrote:
> > On Wed, Mar 05, 2025 at 03:02:29PM -0400, Jason Gunthorpe wrote:
> > > On Wed, Mar 05, 2025 at 10:04:25AM +0100, Stefano Garzarella wrote:
> > > > Jason suggested the send_recv() ops [2], which I liked, but if you prefer to
> > > > avoid that, I can restore what we did in v1 and replace the
> > > > TPM_CHIP_FLAG_IRQ hack with your point 2 (or use TPM_CHIP_FLAG_IRQ if you
> > > > think it is fine).
> > > 
> > > I think it is a pretty notable simplification for the driver as it
> > > does not need to implement send, status, req_canceled and more ops.
> > > 
> > > Given the small LOC on the core side I'd call that simplification a
> > > win..
> > 
> > I'm sorry to disagree with you on this but adding a callback for
> > one leaf driver is not what I would call "a win" :-)
> 
> IIUC in the ftpm driver (tpm_ftpm_tee.c) we could also use send_recv() and
> save a memcpy() to a temporally buffer (pvt_data->resp_buf) and also that 4k
> buffer allocated with the private data of the driver.
> 
> BTW if you agree, for now I'll do something similar of what we do in the
> ftpm driver (which would be what Jarkko recommended - status() returns 0,
> .req_complete_mask = 0, .req_complete_val = 0) and we can discuss
> send_recv() in a new series where I can include changes for the ftpm driver
> too, to see whether it makes sense or not.
> 
> WDYT?

Yeah, that would work. Althought not related to this callback interface
per se, also tpm-dev-common.c is one example (in a way).

> 
> Thanks,
> Stefano

BR, Jarkko