Re: [PATCH] drm/i915: add missing condition for committing planes on crtc

Daniel Vetter
2016-05-09T07:41:12Z

On Fri, May 06, 2016 at 01:52:58PM +0300, Ville Syrjälä wrote:
> On Thu, May 05, 2016 at 03:04:54PM +0100, Lionel Landwerlin wrote:
> > On 04/05/16 15:30, Ville Syrjälä wrote:
> > > On Wed, May 04, 2016 at 02:40:34PM +0100, Lionel Landwerlin wrote:
> > >> We are currently missing the color management update condition to
> > >> commit planes on crtc.
> > >>
> > >> v2: add comment about moving the commit of color management registers
> > >> to an async worker
> > >>
> > >> v3: Commit color management register right after vblank
> > >>
> > >> Fixes: 20a34e78f0d7 (drm/i915: Update color management during vblank evasion.)
> > >> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > >> Cc: Jani Nikula <jani.nikula@intel.com>
> > >> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > >> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > >> Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
> > >> ---
> > >> drivers/gpu/drm/i915/intel_display.c | 5 +++++
> > >> 1 file changed, 5 insertions(+)
> > >>
> > >> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > >> index 45c218d..c6acfe5 100644
> > >> --- a/drivers/gpu/drm/i915/intel_display.c
> > >> +++ b/drivers/gpu/drm/i915/intel_display.c
> > >> @@ -13688,6 +13688,11 @@ static int intel_atomic_commit(struct drm_device *dev,
> > >>
> > >> if (dev_priv->display.optimize_watermarks)
> > >> dev_priv->display.optimize_watermarks(intel_cstate);
> > >> +
> > >> + if (crtc->state->color_mgmt_changed) {
> > >> + intel_color_set_csc(crtc->state);
> > > As I said earlier, csc shouldn't be here, at least on pch
> > > platforms. And someone should actually double check whether
> > > vlv/chv have double buffered csc registers or not. Oh and
> > > with these frankensocs the double buffering scheme used
> > > (if any) might be totally crazy, like it is for the pipe B
> > > primary plane scaler on chv. A fact which the spec fails
> > > to explain IIRC. So I'd recommend poking at the hardware
> > > to figure out how it actually works.
> >
> > Where would you put this for pch platforms?
>
> Where you tried to put it originally.
>
> > If this patch is wrong the surely the content of intel_begin_crtc_commit
> > is too right?
>
> Nope, looks correct to me. Everything in there is double buffered
> AFAICS.
>
> >
> > I'm also struggling to understand why the double buffering of the CSC
> > registers matters.
> > Most people will want to configure this at the same time they configure
> > the gamma/degamma
> > LUTs to achieve color management and if the LUTs aren't double buffered
> > then why is it
> > relevant for the CSC?
>
> We want the update to be atomic, for every piece of hardware affecting
> the ouptut of the pipe. Otherwise it's going to look like crap.
>
> For registers that are double buffered on vblank the atomicity can be
> achieved by arming the updates for everything right after evading
> the vblank.
>
> For single buffered registers we'd need to write the registers during
> vblank. But since we suck and can't do that, simply writing them
> somewhere is the best we can do.

I really need to unlazy and type in my generic vblank workers ...
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation