On 01/10/2012 04:20 AM, Daniel Vetter wrote: > On Wed, Jan 04, 2012 at 07:40:45PM +0100, Daniel Vetter wrote: >> Two things seem to do the trick on my ivb machine here: >> - prevent the gt from powering down while waiting for seqno >> notification interrupts by grabbing the force_wake in get_irq (and >> dropping it in put_irq again). >> - ordering writes from the ring's CS by reading a CS register, ACTHD >> seems to work. >> >> Only the blt&bsd ring on ivb seem to be massively affected by this, >> but for paranoia do this dance also on the render ring and on snb >> (i.e. all gpus with forcewake). >> >> Tested with Eric's glCopyPixels loop which without this patch scores a >> missed irq every few seconds. >> >> This patch needs my forcewake rework to use a spinlock instead of >> dev->struct_mutex. >> >> v2: Improve the comment per Eugeni Dodonov's suggestion. >> >> Cc: stable at kernel.org >> Cc: Eric Anholt<eric at anholt.net> >> Cc: Kenneth Graunke<kenneth at whitecape.org> >> Cc: Eugeni Dodonov<eugeni.dodonov at intel.com> >> Tested-by: Eugeni Dodonov<eugeni.dodonov at intel.com> >> Reviewed-by: Eugeni Dodonov<eugeni.dodonov at intel.com> >> Signed-Off-by: Daniel Vetter<daniel.vetter at ffwll.ch> > > From the internal doc "SNB GT PM Programming Guide", Section 4.3.1: > > "GT does not generate interrupts while in RC6 (by design)" > > It talks about the PM interrupt but I think this might also apply to > interrupts in general. So I think we should apply the voodoo patch also to > snb. > > My current working theory is hw engineers changed the way hwstam writes > are generated wrt to the read/write/irq pipeline on ivb and we've only > been lucky that it syncs out everything on snb before the gpu goes into > deep sleep states. > -Daniel Daniel, This is a good find! Your patch looked good to me in the first place, but with this extra bit of information, I believe it all the more. It's simple and it makes a lot of sense. FWIW, Reviewed-by: Kenneth Graunke <kenneth at whitecape.org> I'm in favor of applying this for Gen7, and I'd be fine with applying it on Gen6 too. At the very least we should experiment with it on Gen6---as Keith said, it might help with some of the mysterious issues we've seen. Worth a try at least. Thanks for your great work here! --Kenneth
