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

Stefano Garzarella
2025-02-28T17:07:52Z

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;
+
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);
--
2.48.1