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

Tom Lendacky
2025-03-03T14:06:49Z

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);