greybus: don't use 0 as an operation id

Stop allowing 0x0000 to be used as an operation id.  That id will be
reserved for use by operations that will return no response message.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>
greybus: get rid of pending operations list

A connection has two lists of operations, and an operation is always
on one or the other of them.  One of them contains the operations
that are currently "in flight".

We really don't expect to have very many in-flight operations on any
given connection (in fact, at the moment it's always exactly one).
So there's no significant performance benefit to keeping these in a
separate list.  An in-flight operation can also be distinguished by
its errno field holding -EINPROGRESS.

Get rid of the pending list, and search all operations rather than
the pending list when looking up a response message's operation.
Rename gb_pending_operation_find() accordingly.

There's no longer any need to remove operations from the pending
list, and the insertion function no longer has anything to do with a
pending list.  Just open code what was the insertion function (it
now has only to do with assigning the operation id).

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>
greybus: make op_cycle atomic (again)

There's no need to protect updating a connections operation id cycle
counter with the operations spinlock.   That spinlock protects
connection lists, which do not interact with the cycle counter.
All that we require is that it gets updated atomically, and we
can express that requirement in its type.

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

Define a new function used to initiate a synchronous operation.
It sends the operation request message and doesn't return until
the response has been received and/or the operation's result
has been set.

This gets rid of the convention that a null callback pointer
signifies a synchronous operation.

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