drm/amdgpu: Detect if amdgpu in IOMMU direct map mode

If host and amdgpu IOMMU is not enabled or IOMMU is pass through mode,
set adev->ram_is_direct_mapped flag which will be used to optimize
memory usage for multi GPU mappings.
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -1097,6 +1097,8 @@ struct amdgpu_device {
 
 	struct amdgpu_reset_control     *reset_cntl;
 	uint32_t                        ip_versions[MAX_HWIP][HWIP_MAX_INSTANCE];
+
+	bool				ram_is_direct_mapped;
 };
 
 static inline struct amdgpu_device *drm_to_adev(struct drm_device *ddev)

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

@@ -30,6 +30,7 @@
 #include <linux/module.h>
 #include <linux/console.h>
 #include <linux/slab.h>
+#include <linux/iommu.h>
 
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_probe_helper.h>
@@ -3382,6 +3383,22 @@ static int amdgpu_device_get_job_timeout_settings(struct amdgpu_device *adev)
 	return ret;
 }
 
+/**
+ * amdgpu_device_check_iommu_direct_map - check if RAM direct mapped to GPU
+ *
+ * @adev: amdgpu_device pointer
+ *
+ * RAM direct mapped to GPU if IOMMU is not enabled or is pass through mode
+ */
+static void amdgpu_device_check_iommu_direct_map(struct amdgpu_device *adev)
+{
+	struct iommu_domain *domain;
+
+	domain = iommu_get_domain_for_dev(adev->dev);
+	if (!domain || domain->type == IOMMU_DOMAIN_IDENTITY)
+		adev->ram_is_direct_mapped = true;
+}
+
 static const struct attribute *amdgpu_dev_attributes[] = {
 	&dev_attr_product_name.attr,
 	&dev_attr_product_number.attr,
@@ -3785,6 +3802,8 @@ int amdgpu_device_init(struct amdgpu_device *adev,
 		queue_delayed_work(system_wq, &mgpu_info.delayed_reset_work,
 				   msecs_to_jiffies(AMDGPU_RESUME_MS));
 
+	amdgpu_device_check_iommu_direct_map(adev);
+
 	return 0;
 
 release_ras_con: