drm/amdgpu: Add vis_vramlimit module parameter

Allow specifying a limit on visible VRAM via a module parameter. This is
helpful for testing performance under visible VRAM pressure.

v2: Add cast to 64-bit (Christian König)
Signed-off-by: NJohn Brooks <john@fastquake.com>
Reviewed-by: NMichel Dänzer <michel.daenzer@amd.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NMichel Dänzer <michel.daenzer@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu.h

@@ -75,6 +75,7 @@
  */
 extern int amdgpu_modeset;
 extern int amdgpu_vram_limit;
+extern int amdgpu_vis_vram_limit;
 extern unsigned amdgpu_gart_size;
 extern int amdgpu_gtt_size;
 extern int amdgpu_moverate;

drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c

@@ -74,6 +74,7 @@
 #define KMS_DRIVER_PATCHLEVEL	0
 
 int amdgpu_vram_limit = 0;
+int amdgpu_vis_vram_limit = 0;
 unsigned amdgpu_gart_size = 256;
 int amdgpu_gtt_size = -1; /* auto */
 int amdgpu_moverate = -1; /* auto */
@@ -121,6 +122,9 @@ int amdgpu_lbpw = -1;
 MODULE_PARM_DESC(vramlimit, "Restrict VRAM for testing, in megabytes");
 module_param_named(vramlimit, amdgpu_vram_limit, int, 0600);
 
+MODULE_PARM_DESC(vis_vramlimit, "Restrict visible VRAM for testing, in megabytes");
+module_param_named(vis_vramlimit, amdgpu_vis_vram_limit, int, 0444);
+
 MODULE_PARM_DESC(gartsize, "Size of PCIE/IGP gart to setup in megabytes (32, 64, etc.)");
 module_param_named(gartsize, amdgpu_gart_size, uint, 0600);
 

drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c

@@ -1099,6 +1099,7 @@ int amdgpu_ttm_init(struct amdgpu_device *adev)
 {
 	uint64_t gtt_size;
 	int r;
+	u64 vis_vram_limit;
 
 	r = amdgpu_ttm_global_init(adev);
 	if (r) {
@@ -1122,6 +1123,13 @@ int amdgpu_ttm_init(struct amdgpu_device *adev)
 		DRM_ERROR("Failed initializing VRAM heap.\n");
 		return r;
 	}
+
+	/* Reduce size of CPU-visible VRAM if requested */
+	vis_vram_limit = (u64)amdgpu_vis_vram_limit * 1024 * 1024;
+	if (amdgpu_vis_vram_limit > 0 &&
+	    vis_vram_limit <= adev->mc.visible_vram_size)
+		adev->mc.visible_vram_size = vis_vram_limit;
+
 	/* Change the size here instead of the init above so only lpfn is affected */
 	amdgpu_ttm_set_active_vram_size(adev, adev->mc.visible_vram_size);