tpm: add support for partial reads

Currently to read a response from the TPM device an application needs
provide big enough buffer for the whole response and read it in one go.
The application doesn't know how big the response it beforehand so it
always needs to maintain a 4K buffer and read the max (4K).
In case if the user of the TSS library doesn't provide big enough
buffer the TCTI spec says that the library should set the required
size and return TSS2_TCTI_RC_INSUFFICIENT_BUFFER error code so that the
application could allocate a bigger buffer and call receive again.
To make it possible in the TSS library, this requires being able to do
partial reads from the driver.
The library would read the 10 bytes header first to get the actual size
of the response from the header, and then read the rest of the response.

This patch adds support for partial reads, i.e. the user can read the
response in one or multiple reads, until the whole response is consumed.
The user can also read only part of the response and ignore
the rest by issuing a new write to send a new command.

Signed-off-by: Tadeusz Struk <tadeusz.struk@intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

1 files changed, 2 insertions, 3 deletions

diff --git a/drivers/char/tpm/tpm-dev.h b/drivers/char/tpm/tpm-dev.h
index a126b575cb8c..1089fc0bb290 100644
--- a/drivers/char/tpm/tpm-dev.h
+++ b/drivers/char/tpm/tpm-dev.h
@@ -9,14 +9,13 @@ struct file_priv {
 	struct tpm_chip *chip;
 	struct tpm_space *space;
 
-	/* Holds the amount of data passed or an error code from async op */
-	ssize_t data_pending;
 	struct mutex buffer_mutex;
-
 	struct timer_list user_read_timer;      /* user needs to claim result */
 	struct work_struct timeout_work;
 	struct work_struct async_work;
 	wait_queue_head_t async_wait;
+	size_t response_length;
+	bool response_read;
 	bool command_enqueued;
 
 	u8 data_buffer[TPM_BUFSIZE];