drm/amd: Disable S/G for APUs when 64GB or more host memory

Users report a white flickering screen on multiple systems that
is tied to having 64GB or more memory.  When S/G is enabled pages
will get pinned to both VRAM carve out and system RAM leading to
this.

Until it can be fixed properly, disable S/G when 64GB of memory or
more is detected.  This will force pages to be pinned into VRAM.
This should fix white screen flickers but if VRAM pressure is
encountered may lead to black screens.  It's a trade-off for now.

Fixes: 81d0bcf99009 ("drm/amdgpu: make display pinning more flexible (v2)")
Cc: Hamza Mahfooz <Hamza.Mahfooz@amd.com>
Cc: Roman Li <roman.li@amd.com>
Cc: <stable@vger.kernel.org> # 6.1.y: bf0207e172703 ("drm/amdgpu: add S/G display parameter")
Cc: <stable@vger.kernel.org> # 6.4.y
Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2735
Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2354
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

1 files changed, 26 insertions, 0 deletions

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index dc0e5227119b..0d602abd32ba 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -1297,6 +1297,32 @@ bool amdgpu_device_need_post(struct amdgpu_device *adev)
 }
 
 /*
+ * On APUs with >= 64GB white flickering has been observed w/ SG enabled.
+ * Disable S/G on such systems until we have a proper fix.
+ * https://gitlab.freedesktop.org/drm/amd/-/issues/2354
+ * https://gitlab.freedesktop.org/drm/amd/-/issues/2735
+ */
+bool amdgpu_sg_display_supported(struct amdgpu_device *adev)
+{
+	switch (amdgpu_sg_display) {
+	case -1:
+		break;
+	case 0:
+		return false;
+	case 1:
+		return true;
+	default:
+		return false;
+	}
+	if ((totalram_pages() << (PAGE_SHIFT - 10)) +
+	    (adev->gmc.real_vram_size / 1024) >= 64000000) {
+		DRM_WARN("Disabling S/G due to >=64GB RAM\n");
+		return false;
+	}
+	return true;
+}
+
+/*
  * Intel hosts such as Raptor Lake and Sapphire Rapids don't support dynamic
  * speed switching. Until we have confirmation from Intel that a specific host
  * supports it, it's safer that we keep it disabled for all.