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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 4/4] drm/simple-kms: Let DRM core send VBLANK events by default
Hi Am 22.01.20 um 09:11 schrieb Daniel Vetter: > On Fri, Jan 17, 2020 at 08:17:10AM +0100, Thomas Zimmermann wrote: >> Hi >> >> Am 17.01.20 um 00:59 schrieb Daniel Vetter: >>> On Thu, Jan 16, 2020 at 05:22:34PM +0000, Emil Velikov wrote: >>>> Hi all, >>>> >>>> On Thu, 16 Jan 2020 at 07:37, Thomas Zimmermann <tzimmermann@xxxxxxx> >>>> wrote: >>>> >>>>>> diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c >>>>>> b/drivers/gpu/drm/drm_atomic_state_helper.c >>>>>> index 7cf3cf936547..23d2f51fc1d4 100644 >>>>>> --- a/drivers/gpu/drm/drm_atomic_state_helper.c >>>>>> +++ b/drivers/gpu/drm/drm_atomic_state_helper.c >>>>>> @@ -149,6 +149,11 @@ void >>>>>> __drm_atomic_helper_crtc_duplicate_state(struct drm_crtc *crtc, >>>>>> /* Self refresh should be canceled when a new update is available >>>>>> */ >>>>>> state->active = drm_atomic_crtc_effectively_active(state); >>>>>> state->self_refresh_active = false; >>>>>> + >>>>>> + if (drm_dev_has_vblank(crtc->dev)) >>>>>> + state->no_vblank = true; >>>>>> + else >>>>>> + state->no_vblank = false; >>>>>> } >>>>>> EXPORT_SYMBOL(__drm_atomic_helper_crtc_duplicate_state); >>>>> >>>>> I think the if/else branches are in the wrong order. >>> >>> Yeah fumbled that. >>> >>>>> But generally speaking, is it really that easy? The xen driver already >>>>> has to work around simple-kms's auto-enabling of no_vblank (see patch >>>>> 4). Maybe this settings interferes with other drivers as well. At least >>>>> the calls for sending fake vblanks should be removed from all affected >>>>> drivers. >>> >>> Hm xen is really special, in that it has a flip complete event, but not a >>> vblank. I think forcing drivers to overwrite stuff in that case makes >>> sense. >>> >>>> I'm not sure if setting no_vblank based on dev->num_crtcs is the correct >>>> thing. >>>> From the original commit and associated description for no_vblank: >>>> >>>> In some cases CRTCs are active but are not able to generating events, at >>>> least not at every frame at it's expected to. >>>> This is typically the case when the CRTC is feeding a writeback >>>> connector... >>> >>> Yeah, but Thomas' series here wants to extend that. And I think if we roll >>> this out the common case will be "no hw vblank", and the writeback special >> >> Default values should usually be 0 for zalloc and static initializers. >> Should we rename no_vblank to has_vblank then? > > Hm, imo feels like hw without vblank is still the uncommon case. I'd leave > this as-is, but also no objections if you feel like repainting :-) Not a bit. ;) > >>> case is going to be the exception to the exception. Yup, patch 1 that >>> updates the docs doesn't reflect that, which is why I'm bringing up more >>> suggestions here around code & semantics of all these pieces to make them >>> do the most reasonable thing for most of the drivers. >>> >>>> Reflects the ability of a CRTC to send VBLANK events.... >>>> >>>> >>>> The proposed handling of no_vblank feels a little dirty, although >>>> nothing better comes to mind. >>>> Nevertheless code seems perfectly reasonable, so if it were me I'd merge >>>> it. >>> >>> The idea with setting it very early is that drivers can overwrite it very >>> easily. Feels slightly dirty, so I guess we could also set it somewhere in >>> the atomic_helper_check function (similar to how we set the various >>> crtc->*_changed flags, but we're not entirely consistent on these either). >>> >>> For the overall thing what feels irky to me is making this no_vblank >>> default logic (however we end up computing it in the end, whether like >>> this or what I suggested) specific to simple pipe helpers feels kinda >>> wrong. Simple pipe tends to have a higher ratio of drivers for hw without >>> vblank support, but by far not the only ones. Having that special case >>> feels confusing to me (and likely will trip up some people, vblank and >>> event handling is already a huge source of confusion in drm). >> >> Making it a default for simple KMS was only the start. I intended to >> cover all drivers at some point. I just didn't want to go through all >> drivers at once. >> >> I guess for the patchset's v3 I'll audit all drivers for the use of >> no_blank and drm_crtc_send_vblank_event(); and convert the possible >> candidates. > > Yeah it's a pain, thanks for volunteering. Just figured the half-step here > is too much in the uncanney valley. If we're going to polish this, let's > do it right (and we have plenty enough drivers to make sure what we pick > will be a solid choice I think). I went through the drivers and updated them. It's the ones covered here plus some more virtual HW. My search heuristic was to look for drivers that call drm_crtc_send_vblank_event() but do not call drm_vblank_init(). Please see v3 of this patchset. It should be pending on this ML. Best regards Thomas > -Daniel > >> >> Best regards >> Thomas >> >>> >>> One idea behind drm_dev_has_vblank() is also that we could formalize a bit >>> all that, at least for the usual case - xen and maybe others being some >>> exceptions as usual (hence definitely not something the core code should >>> handle). >>> >>> Cheers, Daniel >>> >> >> -- >> Thomas Zimmermann >> Graphics Driver Developer >> SUSE Software Solutions Germany GmbH >> Maxfeldstr. 5, 90409 Nürnberg, Germany >> (HRB 36809, AG Nürnberg) >> Geschäftsführer: Felix Imendörffer >> > > > > -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Felix Imendörffer Attachment:
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