Quoting Ville Syrjälä (2018-05-25 16:43:42) > On Fri, May 25, 2018 at 04:20:07PM +0100, Chris Wilson wrote: > > Quoting Ville Syrjala (2018-05-24 20:04:06) > > > From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > > > > > > Let's suppress the underruns around every modeset sequence instead > > > of trying to avoid it. Planes are disabled at this point anyway so > > > we don't really gain anything from keeping the underrun reporting > > > enabled. Also for PCH ports we already suppress all underruns here > > > anyway so trying avoid it for the CPU eDP doesn't seem all that > > > important. > > > > > > Maybe this gets rid of some lingering spurious underruns? > > > > I'll bite. Isn't the reason for enabling underrung report for the > > modeset itself to detect errors in our sequence? > > In theory CPU FIFO underruns shouldn't happen until we have some planes > enabled. Otherwise we have no data going through the FIFOs and thus > reporting an underrun isn't particularly sane. That doesn't stop gen2 > from doing it though, but gen3+ seem to follow the more reasonable > interpretation of what a FIFO underrun means. Makes sense. > I suppose PCH FIFO underruns are a bit different as there is data flowing > as soon as the CPU pipe starts running, whether or not any planes have > been enabled. So those could certainly indicate some kind of programming > sequence error. Or it could just be totally expected that we start the > PCH side of the pipe first and there's a small bit of time when the CPU > pipe isn't yet pushing out pixels, and that's when the PCH side reports > the underrun. > > > > > How certain are we that these are hw limitations vs sw bugs? > > To the best of my knowledge we are reasonably close to the sequence > listed in bspec. And while it's at least theoretically possible that > there's some change we could make to eliminate the underruns I don't > suppose anyone has the time or energy to try out all possible > variations. > > And as long as the underrun (even if it's real) has vanished by the > time we enable the planes I think we are reasonably safe wrt. getting > the correct looking output to the user's display. Also makes sense. And if glitches during modesetting itself, we hope nobody complains ;) Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
