Re: [PATCH v2 2/4] tpm: support devices with synchronous send()

[Jarkko Sakkinen <jarkko@kernel.org>]

On Tue, Apr 08, 2025 at 10:32:06AM +0200, Stefano Garzarella wrote:
> From: Stefano Garzarella <sgarzare@redhat.com>
> 
> Some devices do not support interrupts and provide a single synchronous
> operation to send the command and receive the response on the same buffer.
> 
> Currently, these types of drivers must use an internal buffer where they
> temporarily store the response between .send() and recv() calls.
> 
> Introduce a new flag (TPM_CHIP_FLAG_SYNC) to support synchronous send().
> If that flag is set by the driver, tpm_try_transmit() will use the send()
> callback to send the command and receive the response on the same buffer
> synchronously. In that case send() return the number of bytes of the
> response on success, or -errno on failure.
> 
> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
> Suggested-by: Jarkko Sakkinen <jarkko@kernel.org>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
>  include/linux/tpm.h              |  1 +
>  drivers/char/tpm/tpm-interface.c | 18 +++++++++++++++---
>  2 files changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> index 2e38edd5838c..0e9746dc9d30 100644
> --- a/include/linux/tpm.h
> +++ b/include/linux/tpm.h
> @@ -350,6 +350,7 @@ enum tpm_chip_flags {
>  	TPM_CHIP_FLAG_SUSPENDED			= BIT(8),
>  	TPM_CHIP_FLAG_HWRNG_DISABLED		= BIT(9),
>  	TPM_CHIP_FLAG_DISABLE			= BIT(10),
> +	TPM_CHIP_FLAG_SYNC			= BIT(11),
>  };
>  
>  #define to_tpm_chip(d) container_of(d, struct tpm_chip, dev)
> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> index 3b6ddcdb4051..9fbe84b5a131 100644
> --- a/drivers/char/tpm/tpm-interface.c
> +++ b/drivers/char/tpm/tpm-interface.c
> @@ -114,8 +114,17 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz)
>  		return rc;
>  	}
>  
> -	/* A sanity check. send() should just return zero on success e.g.
> -	 * not the command length.
> +	/* Synchronous devices return the response directly during the send()
> +	 * call in the same buffer.
> +	 */

Nit:

/*
 * ...

It's wrong in the existing comment.

> +	if (chip->flags & TPM_CHIP_FLAG_SYNC) {
> +		len = rc;
> +		rc = 0;
> +		goto out_send_sync;
> +	}
> +
> +	/* A sanity check. send() of asynchronous devices should just return
> +	 * zero on success e.g. not the command length.
>  	 */
>  	if (rc > 0) {
>  		dev_warn(&chip->dev,
> @@ -151,7 +160,10 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz)
>  	if (len < 0) {
>  		rc = len;
>  		dev_err(&chip->dev, "tpm_transmit: tpm_recv: error %d\n", rc);
> -	} else if (len < TPM_HEADER_SIZE || len != be32_to_cpu(header->length))
> +		return rc;
> +	}
> +out_send_sync:

out_sync would be sufficient

> +	if (len < TPM_HEADER_SIZE || len != be32_to_cpu(header->length))
>  		rc = -EFAULT;
>  
>  	return rc ? rc : len;
> -- 
> 2.49.0
> 

BR, Jarkko