Bad caching of the scratch pixmap

[Michel Dänzer]

On Mit, 2013-04-17 at 10:27 -0600, Daniel Drake wrote: 
> On Wed, Apr 17, 2013 at 1:34 AM, Michel Dänzer <michel at daenzer.net> wrote:
> > Possibly. E.g. I see that mrvlPrepareAccess() returns TRUE but doesn't
> > set pPix->devPrivate.ptr.
> 
> Easy enough to add:    pPix->devPrivate.ptr = pPixSurf->pVirtAddr;
> 
> However, PrepareAccess() doesn't get called on this pixmap. Lets see why:
> 
> When the pixmap was created (in mrvlExaCreatePixmap2), because the BPP
> of this pixmap is 1, it apparently cannot be accelerated. So no GPU
> object is created, the pixmap memory is allocated using simple
> malloc().
> 
> Then we reach exaModifyPixmapHeader_driver() which is called after the
> pixmap is created. pPixData is NULL, so pExaPixmap->sys_ptr is set as
> NULL too.
> 
> Later when we try to fill this pixmap (via exaPolyFillRect and so on),
> we reach ExaDoPrepareAccess, which does:
> 
>     has_gpu_copy = exaPixmapHasGpuCopy(pPixmap);
> 
>     if (has_gpu_copy && pExaPixmap->fb_ptr) {
>         pPixmap->devPrivate.ptr = pExaPixmap->fb_ptr;
>         ret = TRUE;
>     }
>     else {
>         pPixmap->devPrivate.ptr = pExaPixmap->sys_ptr;
>         ret = FALSE;
>     }
> 
> exaPixmapHasGpuCopy() calls into mrvlPixmapIsOffscreen(), which
> returns FALSE, indicating that no acceleration is possible with this
> pixmap.
> 
> So has_gpu_copy is FALSE and we set devPrivate.ptr to
> pExaPixmap->sys_ptr, which is NULL.
> 
> Then we try to draw with that pointer, oops (the backtrace in the
> previous mail shows that pixman is asked to draw to destination
> address 0x0).
> 
> I cannot see a way to make sys_ptr have a non-NULL value in this case
> without having implemented ModifyPixmapHeader.

That's quite possible. TBH I don't know if the EXA 'driver' model can be
made to work at all anymore, as the last EXA development effort a couple
of years ago was focused on the 'mixed' model (enabled by the
EXA_MIXED_PIXMAPS flag). 

-- 
Earthling Michel Dänzer           |                   http://www.amd.com
Libre software enthusiast         |          Debian, X and DRI developer