On Mon, Jul 06, 2015 at 04:23:23PM -0300, Paulo Zanoni wrote: > 2015-07-06 12:04 GMT-03:00 Daniel Vetter <daniel@xxxxxxxx>: > > On Mon, Jul 06, 2015 at 03:50:49PM +0300, Ville Syrjälä wrote: > >> On Mon, Jul 06, 2015 at 02:42:02PM +0200, Daniel Vetter wrote: > >> > Especially for workarounds which is stuff that's almost impossible to > >> > verify: The initial state from the firmware on boot-up and after > >> > resume could be different, which will hide bugs when we do an RMW > >> > cycle. > >> > >> If you're really worried about that then we should then explicitly > >> initialize all the registers that might affect stuff. > >> > >> For a bunch of GT registers we could just do a GPU reset at driver > >> init. That that won't help with UCGCTL and such. > >> > >> I'm also worried that if we don't use RMWs for early parts, the hardware > >> folks may still change the default for some ofhte other bits, and then > >> we end up clobbering those. > > > > The point is that we'll at least consistently clobber them, which is the > > important part. Chasing a bug which only happens when you freshly boot but > > not after the first gpu reset (or first resume or the other way round or > > whatever) is not fun at all. > > I think there are possibly other ways to be consistent. We could, for > example, save the values which we think are correct at boot - even if > we rely on the BIOS - and then (optionally) check them at every resume > or runtime resume. Maybe there are even other ideas for that. > > But I do see the value in what you're doing, even though I'm also > afraid of the possible bugs brought by it, and I like the idea of > starting this with new gens only. If you decide to keep this strategy, > can you please print on debugfs when the RMW value is different from > the non-RMW value? We have a few testcases somewhere which try to make sure the w/a stick after the usual suspects. Unfortunately the kernel instrumentation is very weak for that (atm it only covers the render ring init w/a we do). We could try to extend that a bit. Or we could start screaming into dmesg if the rmw has an effect, like you're suggesting. -Daneil -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
