[PATCH v4 2/4] tpm: support devices with synchronous send()

[Stefano Garzarella]

From: Stefano Garzarella <sgarz...@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 <j...@ziepe.ca>
Suggested-by: Jarkko Sakkinen <jar...@kernel.org>
Reviewed-by: Jarkko Sakkinen <jar...@kernel.org>
Signed-off-by: Stefano Garzarella <sgarz...@redhat.com>
---
v4:
- added Jarkko's R-b
v3:
- fixed comment style [Jarkko]
- renamend `out_send_sync` label to `out_sync` [Jarkko]
---
 include/linux/tpm.h              |  1 +
 drivers/char/tpm/tpm-interface.c | 20 +++++++++++++++++---
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 7ac390ec89ce..681661c93869 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -351,6 +351,7 @@ 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..3dc06836f932 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -114,8 +114,19 @@ 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_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 +162,10 @@ 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_sync:
+       if (len < TPM_HEADER_SIZE || len != be32_to_cpu(header->length))
                rc = -EFAULT;
 
        return rc ? rc : len;
-- 
2.49.0