On Fri, Feb 24, 2017 at 12:09:51PM -0800, Manasi Navare wrote: > Hi Daniel, > > We have ACKs on the userspace design from both Adams and Eric. > Is this enough to merge the kernel patches? > > I spoke to Eric briefly about this and he gave me a verbal r-b as well. > He said the userspace patches cant get merged unless DRM patches are merged. > > So what should be some of our next steps here? Still needs review on the kernel patches themselves, iirc Jani still had some opens on that. But I was out of the loop for 2 weeks :-) -Daniel Thanks for merging the 1st patch in the kernel series. Are there any opens on the 2nd patch (the i915 patch)? I wanted to actually respin the 2nd patch to add reset for intel_dp->lane_count on the link training failure so that it doesn't accidently retrain the link with the stale/failed values. Regards Manasi > > Regards > Manasi > > > On Mon, Feb 13, 2017 at 01:05:17PM -0800, Eric Anholt wrote: > > Martin Peres <martin.peres@xxxxxxxxxxxxxxx> writes: > > > > > On 06/02/17 17:50, Martin Peres wrote: > > >> On 03/02/17 10:04, Daniel Vetter wrote: > > >>> On Fri, Feb 03, 2017 at 01:30:14AM +0200, Martin Peres wrote: > > >>>> On 01/02/17 22:05, Manasi Navare wrote: > > >>>>> On Wed, Feb 01, 2017 at 11:58:16AM -0800, Eric Anholt wrote: > > >>>>>> Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx> writes: > > >>>>>> > > >>>>>>> On Tue, 31 Jan 2017, Eric Anholt <eric@xxxxxxxxxx> wrote: > > >>>>>>>> Martin Peres <martin.peres@xxxxxxxxxxxxxxx> writes: > > >>>>>>>> > > >>>>>>>>> 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> > > >>>>>>>> If I understand this right, there are two failure modes > > >>>>>>>> being > > >>>>>>>> handled: > > >>>>>>>> > > >>>>>>>> 1) A mode that won't actually work because the link isn't > > >>>>>>>> good enough. > > >>>>>>>> > > >>>>>>>> 2) A mode that should work, but link parameters were too > > >>>>>>>> optimistic and if we just ask the kernel to set the mode > > >>>>>>>> again it'll use more conservative parameters that work. > > >>>>>>>> > > >>>>>>>> This patch seems good for 2). For 1), the > > >>>>>>>> drmmode_set_mode_major is going to set our old mode back. > > >>>>>>>> Won't the modeset then fail to link train again, and bring > > >>>>>>>> us back into this loop? The only escape that I see would > > >>>>>>>> be some other userspace responding to the advertised mode > > >>>>>>>> list changing, and then asking X to modeset to something > > >>>>>>>> new. > > >>>>>>>> > > >>>>>>>> To avoid that failure busy loop, should we re-fetching > > >>>>>>>> modes at this point, and only re-setting if our mode still exists? > > >>>>>>> Disclaimer: I don't know anything about the internals of the > > >>>>>>> modesetting driver. > > >>>>>>> > > >>>>>>> Perhaps we can identify the two cases now, but I'd put this > > >>>>>>> more > > >>>>>>> generally: if the link status has gone bad, it's an > > >>>>>>> indicator to userspace that the circumstances may have > > >>>>>>> changed, and userspace should query the kernel for the list > > >>>>>>> of available modes again. It should no longer trust > > >>>>>>> information obtained prior to getting the bad link status, > > >>>>>>> including the current mode. > > >>>>>>> > > >>>>>>> But specifically, I think you're right, and AFAICT asking > > >>>>>>> for the list of modes again is the only way for the > > >>>>>>> userspace to distinguish between the two cases. I don't > > >>>>>>> think there's a shortcut for deciding the current mode is > > >>>>>>> still valid. > > >>>>>> To avoid the busy-loop problem, I think I'd like this patch > > >>>>>> to > > >>>>>> re-query > > >>>>>> the kernel to ask about the current mode list, and only try to re-set > > >>>>>> the mode if our mode is still there. > > >>>>>> > > >>>>>> If the mode isn't there, then it's up to the DE to take action in > > >>>>>> response to the notification of new modes. If you don't have a DE to > > >>>>>> take appropriate action, you're kind of out of luck. > > >>>>>> > > >>>>>> As far as the ABI goes, this seems fine to me. The only concern I had > > >>>>>> about ABI was having to walk all the connectors on every uevent to see > > >>>>>> if any had gone bad -- couldn't we have a flag of some sort about what > > >>>>>> the uevent indicates? But uevents should be super rare, so I'd say > > >>>>>> the > > >>>>>> kernel could go ahead with the current plan. > > >>>>> Yes I agree. The kernel sets the link status BAD as soona s link > > >>>>> training fails > > >>>>> but does not prune the modes until a new modelist is requested by > > >>>>> the userspace. > > >>>>> So this patch should re query the mode list as soon as it sees the > > >>>>> link status > > >>>>> BAD in order for the kernel to validate the modes again based on new > > >>>>> link > > >>>>> paarmeters and send a new mode list back. > > >>>> Seems like a bad behaviour from the kernel, isn't it? It should return > > >>>> immediatly > > >>>> if the mode is gonna be pruned :s > > >>> The mode list pruning isn't relevant for modeesets, the kernel doesn't > > >>> validate requested modes against that. The mode list is purely for > > >>> userspace's information. Which means updating it only when userspace asks > > >>> for it is fine. > > >> > > >> Hmm, ok. Fair enough! > > >> > > >>> I also thought some more about the loop when we're stuck on BAD, and I > > >>> think it shouldn't happen: When the link goes BAD we update the link > > >>> parameter values to the new limits, and the kernel will reject any mode > > >>> that won't fit anymore. Of course you might be unlucky, and the new link > > >>> limits are also not working, but eventually you're stuck at the "you're > > >>> link is broken, sry" stage, where the kernel rejects everything :-) > > >>> > > >>> So I think the busy-loop has strictly a limited amount of time until it > > >>> runs out of steam. > > >> > > >> OK, I have given it more thoughts and discussed with Ville and Chris IRL or > > >> on IRC. > > >> > > >> My current proposal is based on the idea that the kernel should reject a > > >> mode > > >> it knows it cannot set. This is already largely tested in real life: Try > > >> setting 4K@60Hz on an HDMI 1.x monitor, it should immediately fail on > > >> prepare(). For this proposal to work, we would need to put in the ABI > > >> that a > > >> driver that sets the link-status to BAD should also make sure that whatever > > >> the userspace does, no infinite loop should be created (by changing the > > >> maximum link characteristics before setting the link-status property). > > >> > > >> Re-probing the list of modes and checking if the mode is still in there is > > >> inherently racy, as a new screen may be plugged between the moment the list > > >> is sent to the userspace and the moment when we try setting the mode. Or > > >> the > > >> DE may also have changed the mode in the mean time and the kernel would > > >> have reduced the limits even more. So, the userspace cannot be expected to > > >> always do the right thing here :s. > > >> > > >> From this point of view, I really do not like the idea of re-probing, since > > >> it increases the delay before the DE can handle the change and it does not > > >> bring any guarantee of working properly. > > >> > > >> Did I miss anything? Any opinions? > > > > > > Any comments on this, Eric? Does it sound logical to you or did I miss > > > something? > > > > > > The kernel patches are stuck until this patch gets in. So far, you look > > > like the only person who would be willing to review this patch (Ajax > > > acked the patch, but that's the extent he was willing to go). > > > > I was just trying to provide review to get the kernel unstuck. The > > kernel should not be blocked until the patch gets lands (this obviously > > isn't the case with ioctls, which *don't* land in userspace until kernel > > does), you just need userspace published and generally agreed that the > > ABI works. > > -- 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
