On Thu, Feb 23, 2017 at 10:02:26AM +0100, Stefan Lengfeld wrote: > Hi Maxime, Hi Ville, > > On Wed, Feb 22, 2017 at 04:52:33PM -0800, Maxime Ripard wrote: > > Hi Ville, Stefan, > > > > On Tue, Feb 21, 2017 at 12:55:01PM +0200, Ville Syrjälä wrote: > > > On Tue, Feb 21, 2017 at 11:00:59AM +0100, Stefan Lengfeld wrote: > > > > > > > > Furthmore most exiting userspace code just passes the value "0" as the > > > > argument. For example DirectFB: > > > > > > > > static const int zero = 0; > > > > [...] > > > > if (ioctl( dfb_fbdev->fd, FBIO_WAITFORVSYNC, &zero )) > > > > > > Again the matrox driver is different. And looks like unichrome might have > > > done something even more exotic with the argument. > > > > > > But I do agree that using this with the kms fbdev implementation could > > > be quite problematic as you can't actually know which crtcs the > > > fb_helper has picked. > > > > I'm not sure what a good solution might be then. Is just waiting for > > always the first crtc acceptable? All the code I could find is passing > > 0 as an argument anyway, so that's effectively the same behaviour > > anyway here. And getting tearing might be a good argument in favour of > > moving to KMS :) > > > > I also vote for the first solution: just waiting for the first enabled > crtc. It's deterministic and userspace can avoid tearing at least for > one crtc. If the system has more active scanouts at the same time with > different timings, userspace has to use the newer kms/drm API. > > It is the same argument as already posted by Michel Dänzer: > > > 2/ Wait for a single vsync event on all active crtcs as Ville Syrjälä > > described here [2] in the optimal implementation. > > FWIW, this seems like a bad idea, since with multiple active CRTCs it > would make it essentially random at which intervals the ioctl returns, > and which CRTCs are in vertical blank when it does. So it would be > useless for both timing and tearing prevention purposes, i.e. more or > less completely useless. > > So I think the implementation (waiting only for the first crtc) of ioctl > FBIO_WAITFORVSYNC is a good enough implementation and works the most > already existing userspace code out there. Also note that integrated panels /should/ be the first connectors in the connector list, which means the first active crtc is most likely the integrated panel (if there is one). That's about as good a default choice as we can make I think, everything else really just needs to get over to doing KMS natively. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
