Subject: bus_space_barrier() [Re: CVS commit: syssrc]
To: Lennart Augustsson <>
From: Jason R Thorpe <>
List: tech-kern
Date: 04/26/2000 08:00:21
On Tue, Apr 25, 2000 at 07:28:15AM -0700, Lennart Augustsson wrote:

 > Module Name:	syssrc
 > Committed By:	augustss
 > Date:		Tue Apr 25 14:28:15 UTC 2000
 > Modified Files:
 > 	syssrc/sys/dev/usb: ohci.c uhci.c
 > Log Message:
 > Insert (very conservative!) bus_space_barrier() calls at all register accesses.
 > The bus_space(9) man page says you've gotta have them...

I want to at least partially revise this part of bus_space(9).  It is, in
fact, the case *right now* that barriers are always implied by bus_space
operations.  This is because for may devices, you would have to do what you
just did; insert barriers everywhere.

What I would like to do is add a __BUS_SPACE_NO_IMPLIED_BARRIERS which
drivers can define which disables the implicit bus_space_barrier() calls
for that source file.  That way a driver could do optimized barriers if
it so chooses.

It would push some complexity into some of the bus.h implementations, but
I don't think it's worth it.

        -- Jason R. Thorpe <>