drm/amdgpu: Take IOMMU remapping into account for p2p checks

when trying to enable p2p the amdgpu_device_is_peer_accessible()
checks the condition where address_mask overlaps the aper_base
and hence returns 0, due to which the p2p disables for this platform

IOMMU should remap the BAR addresses so the device can access
them. Hence check if peer_adev is remapping DMA

v5: (Felix, Alex)
- fixing comment as per Alex feedback
- refactor code as per Felix

v4: (Alex)
- fix the comment and description

v3:
- remove iommu_remap variable

v2: (Alex)
- Fix as per review comments
- add new function amdgpu_device_check_iommu_remap to check if iommu
  remap
Signed-off-by: Rahul Jain <Rahul.Jain@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_device.c

@@ -3957,6 +3957,27 @@ static void amdgpu_device_check_iommu_direct_map(struct amdgpu_device *adev)
 		adev->ram_is_direct_mapped = true;
 }
 
+#if defined(CONFIG_HSA_AMD_P2P)
+/**
+ * amdgpu_device_check_iommu_remap - Check if DMA remapping is enabled.
+ *
+ * @adev: amdgpu_device pointer
+ *
+ * return if IOMMU remapping bar address
+ */
+static bool amdgpu_device_check_iommu_remap(struct amdgpu_device *adev)
+{
+	struct iommu_domain *domain;
+
+	domain = iommu_get_domain_for_dev(adev->dev);
+	if (domain && (domain->type == IOMMU_DOMAIN_DMA ||
+		domain->type ==	IOMMU_DOMAIN_DMA_FQ))
+		return true;
+
+	return false;
+}
+#endif
+
 static const struct attribute *amdgpu_dev_attributes[] = {
 	&dev_attr_pcie_replay_count.attr,
 	NULL
@@ -6151,18 +6172,24 @@ bool amdgpu_device_is_peer_accessible(struct amdgpu_device *adev,
 				      struct amdgpu_device *peer_adev)
 {
 #ifdef CONFIG_HSA_AMD_P2P
-	uint64_t address_mask = peer_adev->dev->dma_mask ?
-		~*peer_adev->dev->dma_mask : ~((1ULL << 32) - 1);
-	resource_size_t aper_limit =
-		adev->gmc.aper_base + adev->gmc.aper_size - 1;
 	bool p2p_access =
 		!adev->gmc.xgmi.connected_to_cpu &&
 		!(pci_p2pdma_distance(adev->pdev, peer_adev->dev, false) < 0);
 
-	return pcie_p2p && p2p_access && (adev->gmc.visible_vram_size &&
-		adev->gmc.real_vram_size == adev->gmc.visible_vram_size &&
-		!(adev->gmc.aper_base & address_mask ||
-		  aper_limit & address_mask));
+	bool is_large_bar = adev->gmc.visible_vram_size &&
+		adev->gmc.real_vram_size == adev->gmc.visible_vram_size;
+	bool p2p_addressable = amdgpu_device_check_iommu_remap(peer_adev);
+
+	if (!p2p_addressable) {
+		uint64_t address_mask = peer_adev->dev->dma_mask ?
+			~*peer_adev->dev->dma_mask : ~((1ULL << 32) - 1);
+		resource_size_t aper_limit =
+			adev->gmc.aper_base + adev->gmc.aper_size - 1;
+
+		p2p_addressable = !(adev->gmc.aper_base & address_mask ||
+				     aper_limit & address_mask);
+	}
+	return is_large_bar && p2p_access && p2p_addressable;
 #else
 	return false;
 #endif