i965: Account for poor address calculations in Haswell CS scratch size.

Curro figured this out by investigating the simulator.  Apparently
there's also a workaround in the Windows driver.  I'm not sure it's
actually documented anywhere.

We were underallocating the scratch buffer by a factor of 128/70.

v2: Rename threads_per_subslice to scratch_ids_per_subslice
    (suggested by Jordan Justen).

Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

src/mesa/drivers/dri/i965/brw_cs.c

@@ -150,9 +150,28 @@ brw_codegen_cs_prog(struct brw_context *brw,
 
    if (prog_data.base.total_scratch) {
       const unsigned subslices = MAX2(brw->intelScreen->subslice_total, 1);
+
+      /* WaCSScratchSize:hsw
+       *
+       * Haswell's scratch space address calculation appears to be sparse
+       * rather than tightly packed.  The Thread ID has bits indicating
+       * which subslice, EU within a subslice, and thread within an EU
+       * it is.  There's a maximum of two slices and two subslices, so these
+       * can be stored with a single bit.  Even though there are only 10 EUs
+       * per subslice, this is stored in 4 bits, so there's an effective
+       * maximum value of 16 EUs.  Similarly, although there are only 7
+       * threads per EU, this is stored in a 3 bit number, giving an effective
+       * maximum value of 8 threads per EU.
+       *
+       * This means that we need to use 16 * 8 instead of 10 * 7 for the
+       * number of threads per subslice.
+       */
+      const unsigned scratch_ids_per_subslice =
+         brw->is_haswell ? 16 * 8 : brw->max_cs_threads;
+
       brw_get_scratch_bo(brw, &brw->cs.base.scratch_bo,
                          prog_data.base.total_scratch *
-                         brw->max_cs_threads * subslices);
+                         scratch_ids_per_subslice * subslices);
    }
 
    if (unlikely(INTEL_DEBUG & DEBUG_CS))