MFC: r218812

MFC: r218812

Fix several issues with the mps(4) driver.

When the driver ran out of DMA chaining buffers, it kept the timeout for
the I/O, and I/O would stall.

The driver was not freezing the device queue on errors.

mps.c:		Pull command completion logic into a separate
		function, and call the callback/wakeup for commands
		that are never sent due to lack of chain buffers.

		Add a number of extra diagnostic sysctl variables.

		Handle pre-hardware errors for configuration I/O.
		This doesn't panic the system, but it will fail the
		configuration I/O and there is no retry mechanism.
		So the device probe will not succeed.  This should
		be a very uncommon situation, however.

mps_sas.c:	Freeze the SIM queue when we run out of chain
		buffers, and unfreeze it when more commands
		complete.

		Freeze the device queue when errors occur, so that
		CAM can insure proper command ordering.

		Report pre-hardware errors for task management
		commands.  In general, that shouldn't be possible
		because task management commands don't have S/G
		lists, and that is currently the only error path
		before we get to the hardware.

		Handle pre-hardware errors (like out of chain
		elements) for SMP requests.  That shouldn't happen
		either, since we should have enough space for two
		S/G elements in the standard request.

		For commands that end with
		MPI2_IOCSTATUS_SCSI_IOC_TERMINATED and
		MPI2_IOCSTATUS_SCSI_EXT_TERMINATED, return them
		with CAM_REQUEUE_REQ to retry them unconditionally.
		These seem to be related to back end, transport
		related problems that are hopefully transient.  We
		don't want to go through the retry count for
		something that is not a permanent error.

		Keep track of the number of outstanding I/Os.

mpsvar.h:	Track the number of free chain elements.

		Add variables for the number of outstanding I/Os,
		and I/O high water mark.

		Add variables to track the number of free chain
		buffers and the chain low water mark, as well as
		the number of chain allocation failures.

		Add I/O state flags and an attach done flag.

git-svn-id: svn://svn.freebsd.org/base/stable/8@218922 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f