linux-kernel - Re: [PATCH 1/2] tpm: add send_recv() op in tpm_class

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Message-ID: <Z-QxH7aDjlixl2gp@kernel.org>
Date: Wed, 26 Mar 2025 18:53:51 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: Jason Gunthorpe <jgg@...pe.ca>, linux-kernel@...r.kernel.org,
	Peter Huewe <peterhuewe@....de>, linux-integrity@...r.kernel.org,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Jens Wiklander <jens.wiklander@...aro.org>,
	Sumit Garg <sumit.garg@...nel.org>
Subject: Re: [PATCH 1/2] tpm: add send_recv() op in tpm_class_ops

On Thu, Mar 20, 2025 at 04:24:32PM +0100, Stefano Garzarella wrote:
> From: Stefano Garzarella <sgarzare@...hat.com>
> 
> Some devices do not support interrupts and provide a single operation
> to send the command and receive the response on the same buffer.
> 
> To support this scenario, a driver could set TPM_CHIP_FLAG_IRQ in the
> chip's flags to get recv() to be called immediately after send() in
> tpm_try_transmit(), or it needs to implement .status() to return 0,
> and set both .req_complete_mask and .req_complete_val to 0.
> 
> In order to simplify these drivers and avoid temporary buffers to be

Simplification can be addressed with no callback changes:

https://lore.kernel.org/linux-integrity/20250326161838.123606-1-jarkko@kernel.org/T/#u

I also noticed that tpm_ftpm_tee initalized req_complete_mask and
req_complete_val explictly while they would be already implicitly
zero.

So it reduces this just a matter of getting rid off the extra
buffer.

> used between the .send() and .recv() callbacks, introduce a new callback
> send_recv(). If that callback is defined, it is called in
> tpm_try_transmit() to send the command and receive the response on
> the same buffer in a single call.

I don't find anything in the commit message addressing buf_len an
cmd_len (vs "just len"). Why two lengths are required?

Not completely rejecting but this explanation is incomplete.

BR, Jarkko