i965: Embrace "unlimited" GTT mmap support

From about kernel 4.9, GTT mmaps are virtually unlimited. A new
parameter, I915_PARAM_MMAP_GTT_VERSION, is added to advertise the
feature so query it and use it to avoid limiting tiled allocations to
only fit within the mappable aperture.

A couple of caveats:

 - fence support is still limited by stride to 262144 and the stride
needs to be a multiple of tile_width (as before, and same limitation as
the current 3D pipeline in hardware)

 - the max_gtt_map_object_size forcing untiled may be hiding a few bugs
in handling of large objects, though none were spotted in piglits.

See kernel commit 4cc6907501ed ("drm/i915: Add I915_PARAM_MMAP_GTT_VERSION
to advertise unlimited mmaps").

v2: Include some commentary on mmap virtual space vs CPU addressable
space.

Signed-off-by: Chris Wilson <[email protected]>
Cc: Kenneth Graunke <[email protected]>
Reviewed-by: Kenneth Graunke <[email protected]>
Reviewed-by: Daniel Vetter <[email protected]>

1 files changed, 2 insertions, 15 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_context.c b/src/mesa/drivers/dri/i965/brw_context.c
index d6f0d7bbcb3..13643930e38 100644
--- a/src/mesa/drivers/dri/i965/brw_context.c
+++ b/src/mesa/drivers/dri/i965/brw_context.c
@@ -1044,21 +1044,6 @@ brwCreateContext(gl_api api,
    brw->urb.max_ds_entries = devinfo->urb.max_ds_entries;
    brw->urb.max_gs_entries = devinfo->urb.max_gs_entries;
 
-   /* Estimate the size of the mappable aperture into the GTT.  There's an
-    * ioctl to get the whole GTT size, but not one to get the mappable subset.
-    * It turns out it's basically always 256MB, though some ancient hardware
-    * was smaller.
-    */
-   uint32_t gtt_size = 256 * 1024 * 1024;
-
-   /* We don't want to map two objects such that a memcpy between them would
-    * just fault one mapping in and then the other over and over forever.  So
-    * we would need to divide the GTT size by 2.  Additionally, some GTT is
-    * taken up by things like the framebuffer and the ringbuffer and such, so
-    * be more conservative.
-    */
-   brw->max_gtt_map_object_size = gtt_size / 4;
-
    if (brw->gen == 6)
       brw->urb.gs_present = false;
 
@@ -1069,6 +1054,8 @@ brwCreateContext(gl_api api,
 
    brw->predicate.state = BRW_PREDICATE_STATE_RENDER;
 
+   brw->max_gtt_map_object_size = screen->max_gtt_map_object_size;
+
    brw->use_resource_streamer = screen->has_resource_streamer &&
       (env_var_as_boolean("INTEL_USE_HW_BT", false) ||
        env_var_as_boolean("INTEL_USE_GATHER", false));