i965: correctly assign SamplerCount of INTERFACE_DESCRIPTOR_DATA

We were dividing by 4 twice.  This also papered over a bug where we
were neglecting to clamp the sampler count to the [0, 16] range.

This should have no functional impact, it only affects prefetching.

v2 [Kenneth Graunke]:
 - Clamp sampler_count to [0, 16] to avoid overflowing the valid values
   for this field.  Write a commit message.

Signed-off-by: Kevin Rogovin <kevin.rogovin@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

diff --git a/src/mesa/drivers/dri/i965/genX_state_upload.c b/src/mesa/drivers/dri/i965/genX_state_upload.c
index 4ccfd4891913c83719e1f3fb52c1dcce781b1631..98f69522de530e16e4e26677d540cd5816253be7 100644 (file)
--- a/src/mesa/drivers/dri/i965/genX_state_upload.c
+++ b/src/mesa/drivers/dri/i965/genX_state_upload.c
@@ -4237,7 +4237,7 @@ genX(upload_cs_state)(struct brw_context *brw)
    const struct GENX(INTERFACE_DESCRIPTOR_DATA) idd = {
       .KernelStartPointer = brw->cs.base.prog_offset,
       .SamplerStatePointer = stage_state->sampler_offset,
-      .SamplerCount = DIV_ROUND_UP(stage_state->sampler_count, 4) >> 2,
+      .SamplerCount = DIV_ROUND_UP(CLAMP(stage_state->sampler_count, 0, 16), 4),
       .BindingTablePointer = stage_state->bind_bo_offset,
       .ConstantURBEntryReadLength = cs_prog_data->push.per_thread.regs,
       .NumberofThreadsinGPGPUThreadGroup = cs_prog_data->threads,