[src/trunk]: src/sys/external/bsd/drm2/include/drm Explain the fields of stru...

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/ecb9080d9ffb
branches:  trunk
changeset: 329551:ecb9080d9ffb
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Wed May 28 16:13:02 2014 +0000

description:
Explain the fields of struct intel_gtt for future reference.

diffstat:

 sys/external/bsd/drm2/include/drm/intel-gtt.h |  36 ++++++++++++++++++++++++++-
 1 files changed, 35 insertions(+), 1 deletions(-)

diffs (57 lines):

diff -r 7967da0233fb -r ecb9080d9ffb sys/external/bsd/drm2/include/drm/intel-gtt.h
--- a/sys/external/bsd/drm2/include/drm/intel-gtt.h     Wed May 28 16:07:58 2014 +0000
+++ b/sys/external/bsd/drm2/include/drm/intel-gtt.h     Wed May 28 16:13:02 2014 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: intel-gtt.h,v 1.2 2014/03/18 18:20:43 riastradh Exp $  */
+/*     $NetBSD: intel-gtt.h,v 1.3 2014/05/28 16:13:02 riastradh Exp $  */
 
 /*-
  * Copyright (c) 2013 The NetBSD Foundation, Inc.
@@ -41,13 +41,47 @@
 #include <drm/drm_agp_netbsd.h>
 
 struct intel_gtt {
+       /*
+        * GMADR, graphics memory address, a.k.a. the `aperture'.
+        * Access to bus addresses in the region starting here are
+        * remapped to physical system memory addresses programmed into
+        * the GTT (or GPU-local memory, for i810 chipsets, depending
+        * on the GTT entries).  This corresponds to a prefix of the
+        * GPU's virtual address space.  The virtual address space may
+        * be larger: in that case, there will be more GTT entries than
+        * pages in the aperture.
+        */
        paddr_t                 gma_bus_addr;
+
+       /*
+        * Number of bytes of system memory stolen by the graphics
+        * device for frame buffer memory (but not for the GTT).  These
+        * pages in memory -- if you know where they are -- can't be
+        * used by the CPU, but they can be programmed into the GTT for
+        * access from the GPU.
+        */
        unsigned int            stolen_size;
+
+       /*
+        * Total number of GTT entries, including entries for the GPU's
+        * virtual address space beyond the aperture.
+        */
        unsigned int            gtt_total_entries;
+
+       /*
+        * Number of GTT entries for pages that we can actually map
+        * into the aperture.
+        */
        unsigned int            gtt_mappable_entries;
+
+       /* Scratch page for unbound GTT entries.  */
        bus_dma_segment_t       gtt_scratch_seg;
        bus_dmamap_t            gtt_scratch_map;
+
+       /* Bus space handle for the GTT itself.  */
        bus_space_handle_t      gtt_bsh;
+
+       /* IOMMU-related quirk for certain chipsets.  */
        bool                    do_idle_maps;
 };