Re: [Intel-gfx] [PATCH 00/12] drm: Put drm_display_mode on diet

Ville Syrjälä
2020-02-21T15:40:38Z

On Fri, Feb 21, 2020 at 03:42:56PM +0100, Daniel Vetter wrote:
> On Fri, Feb 21, 2020 at 12:43 PM Ville Syrjälä
> <ville.syrjala@linux.intel.com> wrote:
> >
> > On Fri, Feb 21, 2020 at 01:32:29PM +0200, Jani Nikula wrote:
> > > On Thu, 20 Feb 2020, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> > > > Looks like getting rid of private_flags is going to be pretty
> > > > straightforward. I'll post patches for that once this first series
> > > > lands.
> > >
> > > Going all in on crtc state? I suppose migrating away from private_flags
> > > could easily start in i915 before that. Seems rather independent.
> > >
> > > I guess it's __intel_get_crtc_scanline() and:
> > >
> > > vblank = &crtc->base.dev->vblank[drm_crtc_index(&crtc->base)];
> > > mode = &vblank->hwmode;
> > >
> > > if (mode->private_flags & I915_MODE_FLAG_GET_SCANLINE_FROM_TIMESTAMP)
> > >
> > > that gives me the creeps in reviewing all that.
> > >
> > > There's also [1] adding new uses for private_flags; I think there were
> > > issues in getting at the right crtc state on some of those paths, but I
> > > forget the exact details. Ideas?
> >
> > I'm just going to move them to the crtc_state and put a copy into the
> > crtc itself for the vblank code. Pretty much a 1:1 replacement.
> > Saves me from having to think ;)
>
> I've looked through the patches, and didn't spot any place where we
> couldn't just get at the full crtc state. Might need some crtc->state
> dereferencing and upcasting and making sure stuff is ordered correctly
> with enable/disable paths of crtc, but nothing to jump over.

swap_state() could easily race with the irq handler. I guess
practically unlikely the old crtc state would disappear before
the irq handler is done, but still seems somewhat dubious.

--
Ville Syrjälä
Intel