[RFC PATCH] drm/amdgpu: add force_sg_display module parameter (v2)

[Alex Deucher]

Add a module parameter to force sg (scatter/gather) display
on APUs.  Normally we allow displays in both VRAM and GTT,
but this option forces displays into GTT so we can explicitly
test more scenarios with GTT.

v2: fix checks

Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
---

For reference since the original patch was buggy.

 drivers/gpu/drm/amd/amdgpu/amdgpu.h        |  2 ++
 drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c    | 12 ++++++++++++
 drivers/gpu/drm/amd/amdgpu/amdgpu_object.c |  3 +++
 3 files changed, 17 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
index 872450a3a164..73d0a0807138 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
@@ -244,6 +244,8 @@ extern int amdgpu_num_kcq;
 #define AMDGPU_VCNFW_LOG_SIZE (32 * 1024)
 extern int amdgpu_vcnfw_log;
 
+extern int amdgpu_force_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 */
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
index 4cf2028b5235..c8975c2da853 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
@@ -943,6 +943,18 @@ MODULE_PARM_DESC(smu_pptable_id,
 	"specify pptable id to be used (-1 = auto(default) value, 0 = use pptable from vbios, > 0 = soft pptable id)");
 module_param_named(smu_pptable_id, amdgpu_smu_pptable_id, int, 0444);
 
+/**
+ * DOC: force_sg_display (int)
+ * Force display buffers into GTT (scatter/gather) memory for APUs.
+ * This is used to force GTT only for displays rather than displaying from
+ * either VRAM (carve out) or GTT.
+ *
+ * Defaults to 0, or disabled.
+ */
+int amdgpu_force_sg_display;
+MODULE_PARM_DESC(force_sg_display, "Force S/G display (0 = off (default), 1 = force display to use GTT) ");
+module_param_named(force_sg_display, amdgpu_force_sg_display, int, 0444);
+
 /* These devices are not supported by amdgpu.
  * They are supported by the mach64, r128, radeon drivers
  */
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
index 981010de0a28..840190dd78e4 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
@@ -1516,6 +1516,9 @@ uint32_t amdgpu_bo_get_preferred_domain(struct amdgpu_device *adev,
 		if (adev->gmc.real_vram_size <= AMDGPU_SG_THRESHOLD)
 			domain = AMDGPU_GEM_DOMAIN_GTT;
 	}
+	if ((domain == (AMDGPU_GEM_DOMAIN_VRAM | AMDGPU_GEM_DOMAIN_GTT)) &&
+	    amdgpu_force_sg_display && adev->mode_info.gpu_vm_support)
+		domain = AMDGPU_GEM_DOMAIN_GTT;
 	return domain;
 }
 
-- 
2.39.1