[PATCH v2 4/4] drm/vc4: Restrict active CTM to one CRTC

[Daniel Vetter]

On Sun, Mar 25, 2018 at 08:14:35PM +0200, Stefan Schake wrote:
> Hey Daniel,
> 
> On Sun, Mar 25, 2018 at 10:01 AM, Daniel Stone <daniel at fooishbar.org> wrote:
> > Hi Stefan,
> >
> > On 25 March 2018 at 02:52, Stefan Schake <stschake at gmail.com> wrote:
> >> +static int vc4_crtc_get_ctm_fifo(struct vc4_dev *vc4)
> >> +{
> >> +       return VC4_GET_FIELD(HVS_READ(SCALER_OLEDOFFS),
> >> +                            SCALER_OLEDOFFS_DISPFIFO);
> >> +}
> >
> > This needs to be managed as a global resource through atomic state
> > objects, rather than checking the current hardware state.
> 
> Do you mean as a property or some such that is accessible to userland
> or merely that this could be raced?
> 
> I haven't had much luck finding examples for resources shared between CRTCs
> in the current tree. My understanding here was that if userland commits
> on CRTC B after a check-only on A, we are no longer bound by the earlier
> result for the check-only. Otherwise, I would have to already commit my
> CTM block to one CRTC at check (possibly check only) time.

https://dri.freedesktop.org/docs/drm/gpu/drm-kms.html#handling-driver-private-state

since you only have one CTM it's a shared resource which internally needs
to be tracked as a driver private thing.

Cheers, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch