[Mesa-dev] [PATCH 2/2] i965: handle gl_PointCoord for Gen4 and Gen5 platform

[Eric Anholt]

On Sun, 19 Feb 2012 13:31:33 +0800, Liu Aleaxander <aleaxander at gmail.com> wrote:
> On Sun, Feb 19, 2012 at 8:54 AM, Eric Anholt <eric at anholt.net> wrote:
> > On Sat, 18 Feb 2012 23:07:32 +0800, Liu Aleaxander <aleaxander at gmail.com> wrote:
> >> +   /*
> >> +    * gl_PointCoord is a FS instead of VS builtin variable, thus is not
> >> +    * included in c->nr_setup_regs. But FS need SF do the interpolation,
> >> +    * so that here padding the interpolation for gl_PointCoord in last.
> >> +    */
> >> +   if (c->key.do_point_coord)
> >> +      c->nr_setup_regs++;
> >
> > So you're writing an extra attribute of setup, but you haven't increased
> > the size of the URB entry.  If the URB full except for pointcoord, you'd
> > end up writing over the next URB entry and probably hanging the GPU.  If
> > you correctly allocate the URB size and that gets reflected in
> > urb_read_length, you should be able to read your new attribute.
> 
> That's maybe the place I don't understand quite well so far. Say, you
> write attributes into URB from SF thread to FS. I did increase the
> urb_read_length in wm_state. Is that the allocation you mean? Should
> I, say, allocate size for extra attributes just for FS in SF stage? If
> so, would you please tell me how? Since if I understand correctly, the
> urb_read_length in SF_STATE is counted from the attributes from VF
> stage. Thus at least urb_read_length in SF stage is not the right
> place for me to touch, right?

urb_entry_size in the SF is the size of what the SF outputs and is what
determines how much space is allocated by brw_urb.c
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