Messages in this thread | | | Subject | Re: linux-4.4 bisected: kwin5 stuck on kde5 loading screen with radeon | From | Mario Kleiner <> | Date | Mon, 25 Jan 2016 14:16:45 +0100 |
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On 01/25/2016 05:15 AM, Michel Dänzer wrote: > On 23.01.2016 00:18, Ville Syrjälä wrote: >> On Fri, Jan 22, 2016 at 12:06:00PM +0900, Michel Dänzer wrote: >>> >>> [ Trimming KDE folks from Cc ] >>> >>> On 21.01.2016 19:09, Daniel Vetter wrote: >>>> On Thu, Jan 21, 2016 at 05:36:46PM +0900, Michel Dänzer wrote: >>>>> On 21.01.2016 16:58, Daniel Vetter wrote: >>>>>> >>>>>> Can you please point me at the vblank on/off jump bug please? >>>>> >>>>> AFAIR I originally reported it in response to >>>>> http://lists.freedesktop.org/archives/dri-devel/2015-August/087841.html >>>>> , but I can't find that in the archives, so maybe that was just on IRC. >>>>> See >>>>> http://lists.freedesktop.org/archives/dri-devel/2016-January/099122.html >>>>> . Basically, I ran into the bug fixed by your patch because the counter >>>>> jumped forward on every DPMS off, so it hit the 32-bit boundary after >>>>> just a few days. >>>> >>>> Ok, so just uncovered the overflow bug. >>> >>> Not sure what you mean by "just", but to be clear: The drm_vblank_on/off >>> counter jumping bug (similar to the bug this thread is about), which >>> exposed the overflow bug, is still alive and kicking in 4.5. It seems >>> to happen when turning off the CRTC: >>> >>> [drm:drm_update_vblank_count] updating vblank count on crtc 0: current=218104694, diff=0, hw=916 hw_last=916 >>> [drm:radeon_get_vblank_counter_kms] crtc 0: dist from vblank start 3 >>> [drm:drm_calc_vbltimestamp_from_scanoutpos] crtc 0 : v 0x7 p(2199,-45)@ 7304.307354 -> 7304.308006 [e 0 us, 0 rep] >>> [drm:radeon_get_vblank_counter_kms] crtc 0: dist from vblank start 3 >>> [drm:drm_update_vblank_count] updating vblank count on crtc 0: current=218104694, diff=16776301, hw=1 hw_last=916 >> >> Not sure what bug we're talking about here, but here the hw counter >> clearly jumps backwards. >> >>> [drm:radeon_get_vblank_counter_kms] Query failed! stat 3 >>> [drm:radeon_get_vblank_counter_kms] Query failed! stat 3 >>> [drm:drm_update_vblank_count] updating vblank count on crtc 1: current=0, diff=0, hw=0 hw_last=0 >>> [drm:radeon_get_vblank_counter_kms] Query failed! stat 3 >>> [drm:radeon_get_vblank_counter_kms] Query failed! stat 3 >>> [drm:drm_update_vblank_count] updating vblank count on crtc 2: current=0, diff=0, hw=0 hw_last=0 >>> [drm:radeon_get_vblank_counter_kms] Query failed! stat 3 >>> [drm:radeon_get_vblank_counter_kms] Query failed! stat 3 >>> [drm:drm_update_vblank_count] updating vblank count on crtc 3: current=0, diff=0, hw=0 hw_last=0 >>> [drm:radeon_get_vblank_counter_kms] Query failed! stat 1 >>> [drm:drm_calc_vbltimestamp_from_scanoutpos] crtc 0 : v 0x1 p(0,0)@ 7304.317140 -> 7304.317140 [e 0 us, 0 rep] >>> [drm:radeon_get_vblank_counter_kms] Query failed! stat 1 >>> [drm:drm_update_vblank_count] updating vblank count on crtc 0: current=234880995, diff=16777215, hw=0 hw_last=1 >> >> Same here. > > At least one of the jumps is expected, because this is around turning > off the CRTC for DPMS off. Don't know yet why there are two jumps back > though. > > >> These things just don't happen on i915 because drm_vblank_off() and >> drm_vblank_on() are always called around the times when the hw counter >> might get reset. Or at least that's how it should be. > > Which is of course the idea of Daniel's patch (which is what I'm getting > the above with) or Mario's patch as well, but clearly something's still > wrong. It's certainly possible that it's something in the driver, but > since calling drm_vblank_pre/post_modeset from the same places seems to > work fine (ignoring the regression discussed in this thread)... Do > drm_vblank_on/off require something else to handle this correctly? > >
I suspect it is because vblank_disable_and_save calls drm_update_vblank_count() unconditionally, even if vblank irqs are already off.
So on a manual display disable -> reenable you get something like
At disable:
Call to dpms-off --> atombios_crtc_dpms(DPMS_OFF) --> drm_vblank_off -> vblank_disable_and_save -> irqs off, drm_update_vblank_count() computes final count.
Then the crtc is shut down and its hw counter resets to zero.
At reenable:
Modesetting -> drm_crtc_helper_set_mode -> crtc_funcs->prepare(crtc) -> atombios_crtc_prepare() -> atombios_crtc_dpms(DPMS_OFF) -> drm_vblank_off -> vblank_disable_and_save -> A pointless drm_update_vblank_count() while the hw counter is already reset to zero --> Unwanted counter jump.
The problem doesn't happen on a pure modeset to a different video resolution/refresh rate, as then we only have one call into atombios_crtc_dpms(DPMS_OFF).
I think the fix is to fix vblank_disable_and_save() to only call drm_update_vblank_count() if vblank irqs get actually disabled, not on no-op calls. I will try that now.
Otherwise kms drivers would have to be careful to never call drm_vblank_off multiple times before calling drm_vblank_on, but the help text to drm_vblank_on() claims that unbalanced calls to these functions are perfectly fine.
-mario
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