drm/amdgpu: Set GTT size equal to TTM mem limit

Use the helper function in TTM to get TTM mem limit and
set GTT size to be equal to TTL mem limit.
Signed-off-by: Mukul Joshi <mukul.joshi@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -244,7 +244,6 @@ extern int amdgpu_sg_display;
 
 #define AMDGPU_VM_MAX_NUM_CTX			4096
 #define AMDGPU_SG_THRESHOLD			(256*1024*1024)
-#define AMDGPU_DEFAULT_GTT_SIZE_MB		3072ULL /* 3GB by default */
 #define AMDGPU_WAIT_IDLE_TIMEOUT_IN_MS	        3000
 #define AMDGPU_MAX_USEC_TIMEOUT			100000	/* 100 ms */
 #define AMDGPU_FENCE_JIFFIES_TIMEOUT		(HZ / 2)

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

@@ -1803,26 +1803,13 @@ int amdgpu_ttm_init(struct amdgpu_device *adev)
 	DRM_INFO("amdgpu: %uM of VRAM memory ready\n",
 		 (unsigned) (adev->gmc.real_vram_size / (1024 * 1024)));
 
-	/* Compute GTT size, either based on 1/2 the size of RAM size
-	 * or whatever the user passed on module init */
-	if (amdgpu_gtt_size == -1) {
-		struct sysinfo si;
-
-		si_meminfo(&si);
-		/* Certain GL unit tests for large textures can cause problems
-		 * with the OOM killer since there is no way to link this memory
-		 * to a process.  This was originally mitigated (but not necessarily
-		 * eliminated) by limiting the GTT size.  The problem is this limit
-		 * is often too low for many modern games so just make the limit 1/2
-		 * of system memory which aligns with TTM. The OOM accounting needs
-		 * to be addressed, but we shouldn't prevent common 3D applications
-		 * from being usable just to potentially mitigate that corner case.
-		 */
-		gtt_size = max((AMDGPU_DEFAULT_GTT_SIZE_MB << 20),
-			       (u64)si.totalram * si.mem_unit / 2);
-	} else {
+	/* Compute GTT size, either based on TTM limit
+	 * or whatever the user passed on module init.
+	 */
+	if (amdgpu_gtt_size == -1)
+		gtt_size = ttm_tt_pages_limit() << PAGE_SHIFT;
+	else
 		gtt_size = (uint64_t)amdgpu_gtt_size << 20;
-	}
 
 	/* Initialize GTT memory pool */
 	r = amdgpu_gtt_mgr_init(adev, gtt_size);