greybus: fix an error message

The error message printed by gb_operation_sync() if the operation
fails is wrong.  Fix it.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>
greybus: set up connection->private properly

The connection->private pointer should refer to a protocol-specific
data structure.  Change two protocol drivers (USB and vibrator) so
they now set this.

In addition, because the setup routine may need access to the
data structure, the private pointer should be set early--as
early as possible.  Make the UART, i2c, and GPIO protocol drivers
set the private pointer earlier.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>
greybus: don't let i2c code assume non-null payload pointer

This is in preparation for an upcoming patch, which makes the
payload pointer be NULL when a message has zero bytes of payload.

It ensures a null payload pointer never gets dereferenced.  To do
this we pass the response structure to gb_i2c_transfer_response()
rather than just its data, and if it's null, returning immediately.

Rearrange the logic in gb_i2c_transfer_operation() a bit.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>
greybus: only record message payload size

An asynchronous operation will want to know how big the response
message it receives is.  Rather than require the sender to record
that information, expose a new field "payload_size" available to
the protocol code for this purpose.

An operation message consists of a header and a payload.  The size
of the message can be derived from the size of the payload, so
record only the payload size and not the size of the whole message.
Reorder the fields in a message structure.

Update the description of the message header structure.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>
greybus: use null pointer for empty payload

Currently message->payload always points to the address immediately
following the header in a message.  If the payload length is 0, this
is not a valid pointer.

Change the code to assign a null pointer to the payload in this
case.  I have verified that no code dereferences the payload pointer
unless the payload is known to have non-zero size.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>