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

[Stefano Garzarella <sgarzare@redhat.com>]

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