drm/vram: Support top-down placement flag

Pinning lots of small buffer objects, such as cursors or sprites, to video
memory can lead to fragmentation, which is a problem for devices with only
a small amount of memory. As a result, framebuffer images might not get
pinned, even though there's enough space available overall.

The flag DRM_GEM_VRAM_PL_FLAG_TOPDOWN marks buffer objects to be pinned at
the high end of video memory. This leaves contiguous space available at
the memory's low end.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20190923172753.26593-2-tzimmermann@suse.de
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>

diff --git a/drivers/gpu/drm/drm_gem_vram_helper.c b/drivers/gpu/drm/drm_gem_vram_helper.c
index 49588de889599299839e46d931b388454dd20f6f..dc7942981f4a15a315573beff79d484895203087 100644 (file)
--- a/drivers/gpu/drm/drm_gem_vram_helper.c
+++ b/drivers/gpu/drm/drm_gem_vram_helper.c
@@ -58,6 +58,7 @@ static void drm_gem_vram_placement(struct drm_gem_vram_object *gbo,
 {
        unsigned int i;
        unsigned int c = 0;
+       u32 invariant_flags = pl_flag & TTM_PL_FLAG_TOPDOWN;
 
        gbo->placement.placement = gbo->placements;
        gbo->placement.busy_placement = gbo->placements;
@@ -65,15 +66,18 @@ static void drm_gem_vram_placement(struct drm_gem_vram_object *gbo,
        if (pl_flag & TTM_PL_FLAG_VRAM)
                gbo->placements[c++].flags = TTM_PL_FLAG_WC |
                                             TTM_PL_FLAG_UNCACHED |
-                                            TTM_PL_FLAG_VRAM;
+                                            TTM_PL_FLAG_VRAM |
+                                            invariant_flags;
 
        if (pl_flag & TTM_PL_FLAG_SYSTEM)
                gbo->placements[c++].flags = TTM_PL_MASK_CACHING |
-                                            TTM_PL_FLAG_SYSTEM;
+                                            TTM_PL_FLAG_SYSTEM |
+                                            invariant_flags;
 
        if (!c)
                gbo->placements[c++].flags = TTM_PL_MASK_CACHING |
-                                            TTM_PL_FLAG_SYSTEM;
+                                            TTM_PL_FLAG_SYSTEM |
+                                            invariant_flags;
 
        gbo->placement.num_placement = c;
        gbo->placement.num_busy_placement = c;
@@ -238,6 +242,14 @@ out:
  * the buffer is pinned at its current location (video RAM or system
  * memory).
  *
+ * Small buffer objects, such as cursor images, can lead to memory
+ * fragmentation if they are pinned in the middle of video RAM. This
+ * is especially a problem on devices with only a small amount of
+ * video RAM. Fragmentation can prevent the primary framebuffer from
+ * fitting in, even though there's enough memory overall. The modifier
+ * DRM_GEM_VRAM_PL_FLAG_TOPDOWN marks the buffer object to be pinned
+ * at the high end of the memory region to avoid fragmentation.
+ *
  * Returns:
  * 0 on success, or
  * a negative error code otherwise.

diff --git a/include/drm/drm_gem_vram_helper.h b/include/drm/drm_gem_vram_helper.h
index 418eb1122861a444e463a4491a6560007d457609..354a9cd358a37cd01f496c4afae1eb3ea05ca801 100644 (file)
--- a/include/drm/drm_gem_vram_helper.h
+++ b/include/drm/drm_gem_vram_helper.h
@@ -19,6 +19,7 @@ struct vm_area_struct;
 
 #define DRM_GEM_VRAM_PL_FLAG_VRAM      TTM_PL_FLAG_VRAM
 #define DRM_GEM_VRAM_PL_FLAG_SYSTEM    TTM_PL_FLAG_SYSTEM
+#define DRM_GEM_VRAM_PL_FLAG_TOPDOWN   TTM_PL_FLAG_TOPDOWN
 
 /*
  * Buffer-object helpers