On Wed, 10 Jan 2018 15:35:36 +0100 Daniel Vetter <dan...@ffwll.ch> wrote:
> On Wed, Dec 20, 2017 at 02:58:14PM -0500, Alex Deucher wrote: > > On Mon, Dec 18, 2017 at 2:38 AM, Pekka Paalanen <ppaala...@gmail.com> > > wrote: > > > On Fri, 15 Dec 2017 15:35:53 -0500 > > > Alex Deucher <alexdeuc...@gmail.com> wrote: > > > > > >> On Fri, Dec 15, 2017 at 2:27 AM, Pekka Paalanen <ppaala...@gmail.com> > > >> wrote: > > >> > On Thu, 14 Dec 2017 10:11:32 -0500 > > >> > Alex Deucher <alexdeuc...@gmail.com> wrote: > > >> > > > >> >> On Thu, Dec 14, 2017 at 6:40 AM, Pekka Paalanen <ppaala...@gmail.com> > > >> >> wrote: > > >> >> > From: Pekka Paalanen <pekka.paala...@collabora.co.uk> > > >> >> > > > >> >> > Hi all, > > >> >> > > > >> >> > this is v5 (to match the numbering of my public branches) of the > > >> >> > libweston user > > >> >> > facing API and infrastructure for supporting shared-CRTC clone mode. > > >> >> > > > >> >> > Previous submission with rationale: > > >> >> > https://lists.freedesktop.org/archives/wayland-devel/2017-October/035604.html > > >> >> > > > >> >> > Design document: > > >> >> > https://phabricator.freedesktop.org/w/wayland/weston/atomic-output-config/ > > >> >> > > > >> >> > The goal: > > >> >> > https://phabricator.freedesktop.org/T7727 > > >> >> > > >> >> FWIW, at least with the DC modesetting code in amdgpu, we can > > >> >> synchronize multiple crtcs to the same timing when the monitors all > > >> >> support the same mode timing or with monitors that have different > > >> >> timings using variable length blanking periods on freesync capable > > >> >> monitors. > > >> > > > >> > Hi Alex, > > >> > > > >> > that's cool. How does userspace take advantage of that, how do you > > >> > configure KMS/atomic to make use of that? Is it supported through > > >> > legacy KMS (non-atomic) as well? > > >> > > >> the driver automatically syncs all heads that it can at modeset time I > > >> think. > > > > > > Ok, but we need strong timing guarantees to be able to use it, just > > > like we have when we have a single CRTC routed to several connectors. > > > Is there such a guarantee that continues not only on initial modeset > > > but through all following flips as well? > > > > The timing is synchronized so in theory the flips should happen during > > the same blanking period. I think atomic may be able to guarantee > > that, but while likely I don't think non-atomic can guarantee it. > > We've discussed this a bit internally at intel, and we'll probably have to > export a property where userspace can request that 1 crtc is ganged to > another one. atomic_check in the kernel can then make sure that's either > the case and reject the modeset, and if the modeset passes, userspace > knows that the driver will make sure the flips will stay in sync forever. > > Without that generic userspace can indeed not make any assumptions, since > different CRTC might have different clock sources and slowly drift. Sounds like a nice plan. Weston cannot take advantage of gen-lock otherwise. Thanks, pq
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