On Fri, Sep 18, 2015 at 07:44:34PM +0100, Chris Wilson wrote: > On Fri, Sep 18, 2015 at 09:37:38PM +0300, Ville Syrjälä wrote: > > On Fri, Sep 18, 2015 at 07:33:50PM +0100, Chris Wilson wrote: > > > On Fri, Sep 18, 2015 at 09:23:11PM +0300, Ville Syrjälä wrote: > > > > On Fri, Sep 18, 2015 at 06:42:17PM +0100, Chris Wilson wrote: > > > > > On Fri, Sep 18, 2015 at 08:03:48PM +0300, ville.syrjala@xxxxxxxxxxxxxxx wrote: > > > > > > From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > > > > > > > > > > > > We have a few users of the raw register acces functions outside > > > > > > intel_uncore.c, so let's just move the functions into intel_drv.h. > > > > > > > > > > I would rather see those external users converted to > > > > > I915_READ_FW/I915_WRITE_FW etc. You will then, no doubt, want to convert > > > > > those _FW macro definitions over to the uncore set. > > > > > > > > > > Also due to how we write and post our accesses, the raw functions can be > > > > > the _relaxed variants. > > > > > > > > Hmm. I think the only difference with the relaxed vs. not would be > > > > potential compiler reordering of memory accesses vs. mmio. So if we > > > > start using the relaxed versions we may need to start sprinkling > > > > barriers around. > > > > > > Yes. We have been working under that assumption (weak ordering of writes), > > > or at least I hope we all have been... > > > > Well, looking at the irq code that uses the _FW, what would prevent the > > compiler from eg. reorder the seqno read to happen before the IIR read? > > Well in practice function calls are involved, so there's a barrier > > there, but say we would want to read the seqno straight from the irq > > handler... > > What seqno read? We definitely don't want to be doing those expensive > reads from an irq handler... Yeah I guess that was a crappy example. Trying to think of a better one, I figure execlist status could be read from memory, but apparently that's just mmio. I guess the context update + ELSP write is something we do from the irq handler, but there are plenty of barriers between those two it seems. Maybe there's no good example here. > > Anyway, I thought we had strongly ordered reads on x64/x32? The cpu won't reoder reads vs. reads, or writes vs. writes for that matter if you ignore the nt stuff and whatnot. But AFAIU the whole point of _relaxed() on x86 is that it allows the compiler to reoder memory vs. mmio any which way it wants. -- Ville Syrjälä Intel OTC _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
