[PATCH 3/4] drm/imx: add FB modifier support

[Lucas Stach]

Am Donnerstag, den 04.05.2017, 10:02 +0100 schrieb Daniel Stone:
> Hi,
> 
> On 4 May 2017 at 09:59, Lucas Stach <l.stach at pengutronix.de> wrote:
> > Am Mittwoch, den 03.05.2017, 18:15 +0100 schrieb Daniel Stone:
> >> What about planes which aren't present in this commit, but are still
> >> taking up a PRE unit? Will they have their PRE stolen, or am I missing
> >> something?
> >
> > Yes, the plane->PRE assignment is configurable by matching different AXI
> > IDs in the PRG. So what's happening here is that we basically construct
> > a new assignment for each commit. Planes without a assigned PRE will
> > revert back to pass-through mode in the PRG on plane commit or plane
> > disable.
> 
> So those other planes are fine/untouched, because the PRE has already
> resolved to linear? Specifically if plane A has a tiled FB, then
> userspace does a commit which _only_ contains plane B (also with a
> tiled FB), and plane B steals the PRE that was previously assigned to
> plane A, then plane A continues displaying just fine? Sorry for the
> stupid questions. :)

If userspace does a commit with only plane B it's going to disable plane
A, right? The PRG/PRE register sets are double buffered (or at least we
always use them in this mode). So if plane B steals the PRE from plane
A, which is going to get disabled, plane A will continue to use the PRE
until the end of frame, then the register set will be latched and the
PRE is switched to plane B for the next frame.

Regards,
Lucas