drm/exynos: Use selected dma_dev default iommu domain instead of a fake one

Instead of allocating a fake IOMMU domain for all Exynos DRM components,
simply reuse the default IOMMU domain of the already selected DMA device.
This allows some design changes in IOMMU framework without breaking IOMMU
support in Exynos DRM.
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_iommu.h

@@ -55,37 +55,12 @@ static inline void __exynos_iommu_detach(struct exynos_drm_private *priv,
 static inline int __exynos_iommu_create_mapping(struct exynos_drm_private *priv,
 					unsigned long start, unsigned long size)
 {
-	struct iommu_domain *domain;
-	int ret;
-
-	domain = iommu_domain_alloc(priv->dma_dev->bus);
-	if (!domain)
-		return -ENOMEM;
-
-	ret = iommu_get_dma_cookie(domain);
-	if (ret)
-		goto free_domain;
-
-	ret = iommu_dma_init_domain(domain, start, size, NULL);
-	if (ret)
-		goto put_cookie;
-
-	priv->mapping = domain;
+	priv->mapping = iommu_get_domain_for_dev(priv->dma_dev);
 	return 0;
-
-put_cookie:
-	iommu_put_dma_cookie(domain);
-free_domain:
-	iommu_domain_free(domain);
-	return ret;
 }
 
 static inline void __exynos_iommu_release_mapping(struct exynos_drm_private *priv)
 {
-	struct iommu_domain *domain = priv->mapping;
-
-	iommu_put_dma_cookie(domain);
-	iommu_domain_free(domain);
 	priv->mapping = NULL;
 }
 
@@ -94,7 +69,9 @@ static inline int __exynos_iommu_attach(struct exynos_drm_private *priv,
 {
 	struct iommu_domain *domain = priv->mapping;
 
-	return iommu_attach_device(domain, dev);
+	if (dev != priv->dma_dev)
+		return iommu_attach_device(domain, dev);
+	return 0;
 }
 
 static inline void __exynos_iommu_detach(struct exynos_drm_private *priv,
@@ -102,7 +79,8 @@ static inline void __exynos_iommu_detach(struct exynos_drm_private *priv,
 {
 	struct iommu_domain *domain = priv->mapping;
 
-	iommu_detach_device(domain, dev);
+	if (dev != priv->dma_dev)
+		iommu_detach_device(domain, dev);
 }
 #else
 #error Unsupported architecture and IOMMU/DMA-mapping glue code