[RFC PATCH 1/3] tpm: add send_recv() op in tpm_class_ops

[Stefano Garzarella <sgarzare@redhat.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
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.

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 | 7 +++++++
 2 files changed, 9 insertions(+)

diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 20a40ade8030..9baf10240a3d 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 cmd_len);
 	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..9a6e4b320a8f 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -82,6 +82,12 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz)
 		return -E2BIG;
 	}
 
+	if (chip->ops->send_recv) {
+		rc = 0;
+		len = chip->ops->send_recv(chip, buf, bufsiz, count);
+		goto out_send_recv;
+	}
+
 	rc = chip->ops->send(chip, buf, count);
 	if (rc < 0) {
 		if (rc != -EPIPE)
@@ -124,6 +130,7 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz)
 
 out_recv:
 	len = chip->ops->recv(chip, buf, bufsiz);
+out_send_recv:
 	if (len < 0) {
 		rc = len;
 		dev_err(&chip->dev, "tpm_transmit: tpm_recv: error %d\n", rc);
-- 
2.48.1