On Thu, 14 Apr 2005 11:33:00 EDT, Alan Stern wrote: >On Wed, 13 Apr 2005, Pete Zaitcev wrote: > >> On Tue, 12 Apr 2005 09:50:15 -0400 (EDT) Alan Stern <[EMAIL PROTECTED]> >> wrote: >> >> > What about the question of making sure that I/O operations complete before >> > starting a delay loop, like this: >> > >> > outw(..., ...); >> > mb(); >> > udelay(10); >> > >> > Is the mb() sufficient to insure that the data will be written to the >> > device before the udelay() call begins? >> >> The mb() has nothing to do with outw() in theory, although implementations >> may accomplish it as a side effect. Just drop the mb(). > >Is it true then, on all architectures, that the hardware will complete the >outw() _before_ the CPU executes the udelay() routine, even without the >mb()? > >Or does it not really matter, because the outw() will complete within a >handful of CPU cycles anyway, long before the 10 us delay is over? > >I want to avoid pathological situations where the hardware reorders the >I/O write to occur _after_ the delay loop. Apparently some architectures >have very loose ordering guarantees for I/O operations with respect to >memory operations.
ppc64 is one arch that does not guarantee ordering without barriers. > >Alan Stern ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
