[Intel-gfx] [PATCH 6/6] drm/i915: New drm crtc property for varying the Crtc size

[Daniel Vetter]

On Thu, Aug 14, 2014 at 7:58 PM, Ville Syrjälä
<ville.syrjala at linux.intel.com> wrote:
> Sure but the user can supply any mode, doesn't have to be on any list.
> And the only sane rule for the frobbing would be that you can (slightly)
> reduce hdisp/vdisp but never expand them so that there will never be any
> extra garbage exposed (and the FB might not be big enough anyway). But
> even reducing hdisp/vdisp by one pixel can be enough to anger the
> hardware if a plane then extends one pixel into the blanking.
>
> This isn't much of a problem for i915 though. The hardware is generally
> good enough to not need it. Double wide and (s)dvo/lvds gang mode are
> the only exception that comes to mind. Even there we just need to make
> pipe src width even, but still that's something we have to account
> when clipping planes.
>
> On older hardware there were generally more restrictions eg. some
> legacy baggage from VGA days which required horizontal timings to
> be multiples of 8. I also "fondly" remember much more magic timing
> restrictions in certain pieces hardware which were something close
> to "if (foo*bar % this == that) frob else don't". IMO these kinds of
> restrictions are too magic to make rejecting the mode an option,
> so frobbing is the lesser of two evils.

Imo the mode list we provide should be reasonable for everyone, and if
you start to add your own modes then I expect the user to do that
adjusting for us. Nowadays there should be very few cases where we
don't provide decent mode lists and where it's not a super-special
embedded thing where you need to configure everything yourself anyway.
So I don't think we should ever adjust the input region for a crtc.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch