[PATCH] drm/amdgpu: don't limit gtt size on apus

[Joshua Ashton]

Since commit 24562523688b ("Revert "drm/amd/amdgpu: set gtt size
according to system memory size only""), the GTT size was limited by
3GiB or VRAM size.

This is problematic on APUs, especially with a small carveout
which can be as low as a fixed 128MiB, as there would be very a limited
3GiB available for video memory.
This obviously does not meet the demands of modern applications.

This patch makes it so the GTT size heuristic always uses 3/4ths of
the system memory size on APUs (limiting the size by 3GiB/VRAM size
only on devices with dedicated video memory).

Fixes: 24562523688b ("Revert drm/amd/amdgpu: set gtt size according to
system memory size only")

Signed-off-by: Joshua Ashton <joshua at froggi.es>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c |  5 +++--
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 12 +++++++++---
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
index 72efd579ec5e..a5a41e9272d6 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
@@ -192,8 +192,9 @@ module_param_named(gartsize, amdgpu_gart_size, uint, 0600);
 
 /**
  * DOC: gttsize (int)
- * Restrict the size of GTT domain in MiB for testing. The default is -1 (It's VRAM size if 3GB < VRAM < 3/4 RAM,
- * otherwise 3/4 RAM size).
+ * Restrict the size of GTT domain in MiB for testing. The default is -1 (On APUs this is 3/4th
+ * of the system memory; on dGPUs this is 3GiB or VRAM sized, whichever is bigger,
+ * with an upper bound of 3/4th of system memory.
  */
 MODULE_PARM_DESC(gttsize, "Size of the GTT domain in megabytes (-1 = auto)");
 module_param_named(gttsize, amdgpu_gtt_size, int, 0600);
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index 4d8f19ab1014..294f26f4f310 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -1865,9 +1865,15 @@ int amdgpu_ttm_init(struct amdgpu_device *adev)
 		struct sysinfo si;
 
 		si_meminfo(&si);
-		gtt_size = min(max((AMDGPU_DEFAULT_GTT_SIZE_MB << 20),
-			       adev->gmc.mc_vram_size),
-			       ((uint64_t)si.totalram * si.mem_unit * 3/4));
+		gtt_size = (uint64_t)si.totalram * si.mem_unit * 3/4;
+		/* If we have dedicated memory, limit our GTT size to
+		 * 3GiB or VRAM size, whichever is bigger
+		 */
+		if (!(adev->flags & AMD_IS_APU)) {
+			gtt_size = min(max(AMDGPU_DEFAULT_GTT_SIZE_MB << 20,
+				adev->gmc.mc_vram_size),
+				gtt_size);
+		}
 	}
 	else
 		gtt_size = (uint64_t)amdgpu_gtt_size << 20;
-- 
2.30.0