[PATCH v2] iommu/rockchip: Add missing set_platform_dma_ops callback

[Steven Price <steven.price@arm.com>]

Similar to exynos, we need a set_platform_dma_ops() callback for proper
operation on ARM 32 bit after recent changes in the IOMMU framework
(detach ops removal). But also the use of a NULL domain is confusing.

Rework the code to have a singleton rk_identity_domain which is assigned
to domain when using an identity mapping rather than "detaching". This
makes the code easier to reason about.

Signed-off-by: Steven Price <steven.price@arm.com>
---
Changes since v1[1]:

 * Reworked the code to avoid a NULL domain, instead a singleton
   rk_identity_domain is used instead. The 'detach' language is no
   longer used.

[1] https://lore.kernel.org/r/20230315164152.333251-1-steven.price%40arm.com

 drivers/iommu/rockchip-iommu.c | 50 ++++++++++++++++++++++++++--------
 1 file changed, 39 insertions(+), 11 deletions(-)

diff --git a/drivers/iommu/rockchip-iommu.c b/drivers/iommu/rockchip-iommu.c
index f30db22ea5d7..437541004994 100644
--- a/drivers/iommu/rockchip-iommu.c
+++ b/drivers/iommu/rockchip-iommu.c
@@ -124,6 +124,7 @@ struct rk_iommudata {
 
 static struct device *dma_dev;
 static const struct rk_iommu_ops *rk_ops;
+static struct iommu_domain rk_identity_domain;
 
 static inline void rk_table_flush(struct rk_iommu_domain *dom, dma_addr_t dma,
 				  unsigned int count)
@@ -980,26 +981,27 @@ static int rk_iommu_enable(struct rk_iommu *iommu)
 	return ret;
 }
 
-static void rk_iommu_detach_device(struct iommu_domain *domain,
-				   struct device *dev)
+static int rk_iommu_identity_attach(struct iommu_domain *identity_domain,
+				    struct device *dev)
 {
 	struct rk_iommu *iommu;
-	struct rk_iommu_domain *rk_domain = to_rk_domain(domain);
+	struct rk_iommu_domain *rk_domain;
 	unsigned long flags;
 	int ret;
 
 	/* Allow 'virtual devices' (eg drm) to detach from domain */
 	iommu = rk_iommu_from_dev(dev);
 	if (!iommu)
-		return;
+		return -ENODEV;
+
+	rk_domain = to_rk_domain(iommu->domain);
 
 	dev_dbg(dev, "Detaching from iommu domain\n");
 
-	/* iommu already detached */
-	if (iommu->domain != domain)
-		return;
+	if (iommu->domain == identity_domain)
+		return 0;
 
-	iommu->domain = NULL;
+	iommu->domain = identity_domain;
 
 	spin_lock_irqsave(&rk_domain->iommus_lock, flags);
 	list_del_init(&iommu->node);
@@ -1011,7 +1013,25 @@ static void rk_iommu_detach_device(struct iommu_domain *domain,
 		rk_iommu_disable(iommu);
 		pm_runtime_put(iommu->dev);
 	}
+
+	return 0;
+}
+
+static struct iommu_domain_ops rk_identity_ops = {
+	.attach_dev = rk_iommu_identity_attach,
+};
+
+static struct iommu_domain rk_identity_domain = {
+	.type = IOMMU_DOMAIN_IDENTITY,
+	.ops = &rk_identity_ops,
+};
+
+#ifdef CONFIG_ARM
+static void rk_iommu_set_platform_dma(struct device *dev)
+{
+	WARN_ON(rk_iommu_identity_attach(&rk_identity_domain, dev));
 }
+#endif
 
 static int rk_iommu_attach_device(struct iommu_domain *domain,
 		struct device *dev)
@@ -1035,8 +1055,9 @@ static int rk_iommu_attach_device(struct iommu_domain *domain,
 	if (iommu->domain == domain)
 		return 0;
 
-	if (iommu->domain)
-		rk_iommu_detach_device(iommu->domain, dev);
+	ret = rk_iommu_identity_attach(&rk_identity_domain, dev);
+	if (ret)
+		return ret;
 
 	iommu->domain = domain;
 
@@ -1050,7 +1071,7 @@ static int rk_iommu_attach_device(struct iommu_domain *domain,
 
 	ret = rk_iommu_enable(iommu);
 	if (ret)
-		rk_iommu_detach_device(iommu->domain, dev);
+		WARN_ON(rk_iommu_identity_attach(&rk_identity_domain, dev));
 
 	pm_runtime_put(iommu->dev);
 
@@ -1061,6 +1082,9 @@ static struct iommu_domain *rk_iommu_domain_alloc(unsigned type)
 {
 	struct rk_iommu_domain *rk_domain;
 
+	if (type == IOMMU_DOMAIN_IDENTITY)
+		return &rk_identity_domain;
+
 	if (type != IOMMU_DOMAIN_UNMANAGED && type != IOMMU_DOMAIN_DMA)
 		return NULL;
 
@@ -1176,6 +1200,7 @@ static int rk_iommu_of_xlate(struct device *dev,
 	iommu_dev = of_find_device_by_node(args->np);
 
 	data->iommu = platform_get_drvdata(iommu_dev);
+	data->iommu->domain = &rk_identity_domain;
 	dev_iommu_priv_set(dev, data);
 
 	platform_device_put(iommu_dev);
@@ -1188,6 +1213,9 @@ static const struct iommu_ops rk_iommu_ops = {
 	.probe_device = rk_iommu_probe_device,
 	.release_device = rk_iommu_release_device,
 	.device_group = rk_iommu_device_group,
+#ifdef CONFIG_ARM
+	.set_platform_dma_ops = rk_iommu_set_platform_dma,
+#endif
 	.pgsize_bitmap = RK_IOMMU_PGSIZE_BITMAP,
 	.of_xlate = rk_iommu_of_xlate,
 	.default_domain_ops = &(const struct iommu_domain_ops) {
-- 
2.39.2