On Thu, Mar 30, 2017 at 04:41:57PM +0300, Ville Syrjälä wrote: > On Thu, Mar 30, 2017 at 03:27:57PM +0200, Daniel Vetter wrote: > > On Thu, Mar 30, 2017 at 2:03 PM, Ville Syrjälä > > <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > > On Wed, Mar 22, 2017 at 09:56:12PM +0100, Daniel Vetter wrote: > > >> If we restrict this helper to only kms drivers (which is the case) we > > >> can look up the correct mode easily ourselves. But it's a bit tricky: > > >> > > >> - All legacy drivers look at crtc->hwmode. But that is update already > > >> at the beginning of the modeset helper, which means when we disable > > >> a pipe. Hence the final timestamps might be a bit off. But since > > >> this is an existing bug I'm not going to change it, but just try to > > >> be bug-for-bug compatible with the current code. This only applies > > >> to radeon&amdgpu. > > >> > > >> - i915 tries to get it perfect by updating crtc->hwmode when the pipe > > >> is off (i.e. vblank->enabled = false). > > >> > > >> - All other atomic drivers look at crtc->state->adjusted_mode. Those > > >> that look at state->requested_mode simply don't adjust their mode, > > >> so it's the same. That has two problems: Accessing crtc->state from > > >> interrupt handling code is unsafe, and it's updated before we shut > > >> down the pipe. For nonblocking modesets it's even worse. > > >> > > >> For atomic drivers try to implement what i915 does. To do that we add > > >> a new hwmode field to the vblank structure, and update it from > > >> drm_calc_timestamping_constants(). > > > > > > i915 clear crtc->hwmode.crtc_clock when turning the crtc off, which > > > this does not do for the new vblank->hwmode. I guess no one should > > > really end up in these codepaths with a disabled crtc, but parts of > > > drm_irq.c sort of look like they're expecting it to happen. > > > > > > So should we have some way to clear out the vblank->hwmode.crtc_clock > > > for disabled crtcs? And then maybe make some of these crtc_clock checks > > > WARN and eventually just nuke it all if it looks like nothing is hitting > > > those? > > > > So the trouble is that with a pile of dpms on/off/on/off you could run > > drm_crtc_vblank_on/off a lot, without ever calling the > > drm_calc_vbltimestamps helper again to re-upload the mode. So I don't > > think we can clear vblank->hwmode.crtc_clock unfortunately in > > drm_crtc_vblank_off. > > I was thinking that we'd just try to avoid making pontetially functional > changes here. Ie. reset where we currently reset, which I think is somewhere > in the atomic commit for i915, but definitely not in drm_crtc_vblank_off(). Hm, sounds like a good idea. I'll try to shuffle things around. Upon re-reading all that stuff I also noticed that atm i915 only calls the helper that would update vblank->hwmode when we do a full modeset, but not when we just fastset. Shouldn't matter, because the hwmode will match, but better safe than sorry. I'll re-read all that stuff again and will try to lock it down fully, like we have now, and remove the i915 crtc->hwmode access maybe entirely while at it. -Daniel > > > > > But what we could do (at least with atomic) is WARN in the vblank > > helper if it's called outside of drm_vblank_on/off ... Not sure how > > useful that is (it won't catch when a driver outright forgets to call > > these) or whether we have enough checks already. Would be a separate > > patch (can do ofc if we agree on what exactly). > > -Daniel > > -- > > Daniel Vetter > > Software Engineer, Intel Corporation > > +41 (0) 79 365 57 48 - http://blog.ffwll.ch > > -- > Ville Syrjälä > Intel OTC -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
