[PATCH] usb: ehci: make HC see up-to-date qh/qtd descriptor ASAP

[Mark Salter]

On Wed, 2011-08-31 at 16:21 +0100, Will Deacon wrote:
> On Wed, Aug 31, 2011 at 02:43:33PM +0100, Mark Salter wrote:
> > On Wed, 2011-08-31 at 09:49 +0100, Will Deacon wrote:
> > > On Wed, Aug 31, 2011 at 01:23:47AM +0100, Chen Peter-B29397 wrote:
> > > > One question: why this write buffer issue did not happen at UP ARM V7 platform, whose dma buffer
> > > > also uncache, but bufferable?
> > > 
> > > Which CPU was on this platform?
> > 
> > Using a 3.1.0-rc4+ kernel on a Pandaboard, and running 'hdparm -t' on a
> > usb disk drive, I see ~5.8MB/s read speed. Same kernel, but passing
> > nosmp on the commandline, I see 20.3MB/s.
> > 
> > Can someone explain why nosmp would make such a difference?
> 
> Oh gawd, that's horrible. I have a feeling it's probably a separate issue
> though, caused by:
> 
> omap_modify_auxcoreboot0(0x200, 0xfffffdff);
> 
> in boot_secondary for OMAP. Unfortunately I have no idea what that line is
> doing because it ends up talking to the secure monitor.

Okay, I may poke around a bit with that to see I can get a better
understanding.

With the patched ehci-q.c, I see no noticeable difference between smp
and nosmp. Both get me around 23.5MB/s with my setup.

--Mark