[Mesa-dev] [PATCH 1/3] i965: Fix shared local memory size for Gen9+.

[Kenneth Graunke]

Skylake changes the representation of shared local memory size:

 Size   | 0 kB | 1 kB | 2 kB | 4 kB | 8 kB | 16 kB | 32 kB | 64 kB |
 -------------------------------------------------------------------
 Gen7-8 |    0 | none | none |    1 |    2 |     3 |     4 |     5 |
 -------------------------------------------------------------------
 Gen9+  |    0 |    1 |    2 |    3 |    4 |     5 |     6 |     7 |

The old formula would substantially underallocate the amount of space.
This fixes GPU hangs on Skylake when running with full thread counts.

Cc: "12.0" <mesa-stable at lists.freedesktop.org>
Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/gen7_cs_state.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/gen7_cs_state.c b/src/mesa/drivers/dri/i965/gen7_cs_state.c
index 750aa2c..aff1f4e 100644
--- a/src/mesa/drivers/dri/i965/gen7_cs_state.c
+++ b/src/mesa/drivers/dri/i965/gen7_cs_state.c
@@ -150,11 +150,16 @@ brw_upload_cs_state(struct brw_context *brw)
    assert(prog_data->total_shared <= 64 * 1024);
    uint32_t slm_size = 0;
    if (prog_data->total_shared > 0) {
-      /* slm_size is in 4k increments, but must be a power of 2. */
-      slm_size = 4 * 1024;
-      while (slm_size < prog_data->total_shared)
-         slm_size <<= 1;
-      slm_size /= 4 * 1024;
+      /* Shared Local Memory Size is specified as powers of two. */
+      slm_size = util_next_power_of_two(prog_data->total_shared);
+
+      if (brw->gen >= 9) {
+         /* Use a minimum of 1kB; turn an exponent of 10 (1024 kB) into 1. */
+         slm_size = ffs(MAX2(slm_size, 1024)) - 10;
+      } else {
+         /* Use a minimum of 4kB; convert to the pre-Gen9 representation. */
+         slm_size = MAX2(slm_size, 4096) / 4096;
+      }
    }
 
    desc[dw++] =
-- 
2.8.3