On Fri, 2004-11-19 at 11:17, Michel DÃnzer wrote:
> On Fri, 2004-11-19 at 00:44 -0600, Kevin O'Brien wrote:
> > On Thu, 2004-11-18 at 03:57, Felix KÃhling wrote:
> > > Am Do, den 18.11.2004 schrieb Kevin O'Brien um 8:03:
> > 
> > Page flipping doesn't work with Merge Frame Buffer, [...]
> 
> Sounds like a bug that should be fixed.
> 
> 

What I see is the contents of the primary display duplicated on the
second.  If there are any hints where to look, I'd be very happy to try
to investigate this.

> > Is there a way to ensure the Radeon blits from top to bottom? 
> 
> Sure, by setting the DST_Y_TOP_TO_BOTTOM bit in the DP_CNTL register.
> Might be a good idea to do that in radeon_cp_dispatch_swap().
> 

Alas, I can't get this to work.  My changes have no effect on the
problem.  I increased the size of BEGIN_RING to hold the two entries
required to do this.  First attempt tried using OUT_RING_REG. Second
attempt was to use two OUT_RING calls.  I also tried adjusting
DP_CNTL_XDIR_YDIR_YMAJOR (based on definitions in DRI.)

> > Since blitting is faster than refresh rate, blitting from the top to
> > bottom should produce a "tear" free display - if the blit begins before
> > start of active display.

> > If the Radeon is blitting from bottom to top, a "tear" would occur if
> > the blit is longer than vertical blank when the active picture meets the
> > blit.
> 
> You're assuming there's no (scheduling, ...) lag between the vertical
> blank and the emission of the buffer swap...
> 

While obviously not a generic solution, I may have a work-around by
using multiple blits:

First blit is the top third.
Second blit is the bottom two thirds.

(Dividing it into two equal halves ALMOST worked - a little noisy on the
top line.)

I now have two 1024x768 windows, one on each head, with no visible
artifacts - with limited testing.

NOTE: this also required a tweak to the X driver to ensure the vertical
sync of the two monitors coincide.




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