Re: [RFC PATCH v2 3/6] tpm: add send_recv() ops in tpm_class_ops

[Tom Lendacky <thomas.lendacky@amd.com>]

On 2/28/25 11:07, Stefano Garzarella wrote:
> 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().
> 
> Instead of abusing TPM_CHIP_FLAG_IRQ, 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.
> 
> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
>  include/linux/tpm.h              | 2 ++
>  drivers/char/tpm/tpm-interface.c | 8 +++++++-
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> index 20a40ade8030..2ede8e0592d3 100644
> --- a/include/linux/tpm.h
> +++ b/include/linux/tpm.h
> @@ -88,6 +88,8 @@ struct tpm_class_ops {
>  	bool (*req_canceled)(struct tpm_chip *chip, u8 status);
>  	int (*recv) (struct tpm_chip *chip, u8 *buf, size_t len);
>  	int (*send) (struct tpm_chip *chip, u8 *buf, size_t len);
> +	int (*send_recv)(struct tpm_chip *chip, u8 *buf, size_t buf_len,
> +			 size_t to_send);
>  	void (*cancel) (struct tpm_chip *chip);
>  	u8 (*status) (struct tpm_chip *chip);
>  	void (*update_timeouts)(struct tpm_chip *chip,
> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> index b1daa0d7b341..4f92b0477696 100644
> --- a/drivers/char/tpm/tpm-interface.c
> +++ b/drivers/char/tpm/tpm-interface.c
> @@ -82,6 +82,9 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz)
>  		return -E2BIG;
>  	}
>  
> +	if (chip->ops->send_recv)
> +		goto out_recv;

It might look a bit cleaner if you issue the send_recv() call here and
then jump to a new label after the recv() call just before 'len' is checked.

Thanks,
Tom

> +
>  	rc = chip->ops->send(chip, buf, count);
>  	if (rc < 0) {
>  		if (rc != -EPIPE)
> @@ -123,7 +126,10 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz)
>  	return -ETIME;
>  
>  out_recv:
> -	len = chip->ops->recv(chip, buf, bufsiz);
> +	if (chip->ops->send_recv)
> +		len = chip->ops->send_recv(chip, buf, bufsiz, count);
> +	else
> +		len = chip->ops->recv(chip, buf, bufsiz);
>  	if (len < 0) {
>  		rc = len;
>  		dev_err(&chip->dev, "tpm_transmit: tpm_recv: error %d\n", rc);