On Fri, Mar 31, 2017 at 05:22:09PM -0700, Eric Anholt wrote: > Manasi Navare <manasi.d.navare@xxxxxxxxx> writes: > > > On Fri, Mar 31, 2017 at 01:08:41PM -0700, Eric Anholt wrote: > >> Manasi Navare <manasi.d.navare@xxxxxxxxx> writes: > >> > >> > On Thu, Mar 30, 2017 at 05:37:55PM -0700, Eric Anholt wrote: > >> >> Martin Peres <martin.peres@xxxxxxxxxxxxxxx> writes: > >> >> > >> >> > On 26/01/17 14:37, Martin Peres wrote: > >> >> >> Despite all the careful planing of the kernel, a link may become > >> >> >> insufficient to handle the currently-set mode. At this point, the > >> >> >> kernel should mark this particular configuration as being broken > >> >> >> and potentially prune the mode before setting the offending connector's > >> >> >> link-status to BAD and send the userspace a hotplug event. This may > >> >> >> happen right after a modeset or later on. > >> >> >> > >> >> >> When available, we should use the link-status information to reset > >> >> >> the wanted mode. > >> >> >> > >> >> >> Signed-off-by: Martin Peres <martin.peres@xxxxxxxxxxxxxxx> > >> >> > > >> >> > The relevant kernel patches have landed in drm-tip about a month ago. > >> >> > > >> >> > Eric, would you mind providing feedback on or merging this patch? > >> >> > >> >> The later discussion has sounded like the kernel will (always) prune the > >> >> mode when we re-query, meaning that it doesn't make any sense to try to > >> >> re-set to the old mode. Is this not the case? > >> > > >> > > >> > No the kernel will simply send a hotplug with link status as bad > >> > and then after that point its userspace driver's responsibility > >> > to check if link status is BAD, retry the same mode and if it fails > >> > then re probe. > >> > >> So the kernel will sometimes allow the same mode to be re-set with the > >> same bpp? > > > > So when userspace driver re-sets the same mode, the kernel will call the > > mode valid function where it will see it can allow the sam mode perhaps > > at a lower bpp now since the link parameters are lowered. > > So the mode which failed at 30 bpp, might still work at 18bpp and is > > better going to a lower resolution. > > The question was whether the kernel will ever allow the same mode at the > same bpp, since that's what this patch tries to do. Yes, this can happen. Doing a full modeset with recomputing clocks and everything behind userspace's back might not be something the kernel driver can pull of with a reasonable amount of effort, hence why we punt to userspace. The interface spec makes this a CAN, not WILL, to allow less unreasonable hw to handle these cases directly in the kernel driver. E.g. plain link-retraining is handled in i915.ko still. -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
