[PATCH 2/2] of: platform: port Linux of_dma_is_coherent

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

In order to correctly handle cache-coherent systems on ARM, we need to
be able to determine whether a device instantiated from DT is DMA
coherent. Port the Linux helper that does this check.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
of_dma_is_coherent is still unused, but it will be used in future.
---
 arch/riscv/Kconfig    |  1 +
 drivers/of/Kconfig    |  4 ++++
 drivers/of/platform.c | 41 +++++++++++++++++++++++++++++++++++++++++
 include/of_address.h  |  6 ++++++
 4 files changed, 52 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index cd7f4abf5694..afbd55aa3e6f 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -10,6 +10,7 @@ config RISCV
 	select COMMON_CLK_OF_PROVIDER
 	select CLKDEV_LOOKUP
 	select HAS_DMA
+	select OF_DMA_DEFAULT_COHERENT
 	select HAVE_PBL_IMAGE
 	select HAVE_PBL_MULTI_IMAGES
 	select HAVE_IMAGE_COMPRESSION
diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
index 7283331ba9ce..4dc40b27f442 100644
--- a/drivers/of/Kconfig
+++ b/drivers/of/Kconfig
@@ -31,6 +31,10 @@ config FEATURE_CONTROLLER_FIXUP
 config OF_ADDRESS_PCI
 	bool
 
+config OF_DMA_DEFAULT_COHERENT
+	# arches should select this if DMA is coherent by default for OF devices
+	bool
+
 config OF_GPIO
 	depends on GPIOLIB
 	depends on OFDEVICE
diff --git a/drivers/of/platform.c b/drivers/of/platform.c
index a9a5d4c2daf2..2b5ad08c124b 100644
--- a/drivers/of/platform.c
+++ b/drivers/of/platform.c
@@ -73,6 +73,47 @@ static void of_device_make_bus_id(struct device_d *dev)
 	}
 }
 
+static struct device_node *of_get_next_dma_parent(const struct device_node *np)
+{
+	struct of_phandle_args args;
+	int ret, index;
+
+	index = of_property_match_string(np, "interconnect-names", "dma-mem");
+	if (index < 0)
+		return of_get_parent(np);
+
+	ret = of_parse_phandle_with_args(np, "interconnects",
+					 "#interconnect-cells",
+					 index, &args);
+	if (ret < 0)
+		return of_get_parent(np);
+
+	return args.np;
+}
+
+/**
+ * of_dma_is_coherent - Check if device is coherent
+ * @np:	device node
+ *
+ * It returns true if "dma-coherent" property was found
+ * for this device in the DT, or if DMA is coherent by
+ * default for OF devices on the current platform and no
+ * "dma-noncoherent" property was found for this device.
+ */
+bool of_dma_is_coherent(struct device_node *node)
+{
+	while (node) {
+		if (of_property_read_bool(node, "dma-coherent"))
+			return true;
+		if (of_property_read_bool(node, "dma-noncoherent"))
+			return false;
+		node = of_get_next_dma_parent(node);
+	}
+
+	return IS_ENABLED(CONFIG_OF_DMA_DEFAULT_COHERENT);
+}
+EXPORT_SYMBOL_GPL(of_dma_is_coherent);
+
 static void of_dma_configure(struct device_d *dev, struct device_node *np)
 {
 	u64 dma_addr, paddr, size = 0;
diff --git a/include/of_address.h b/include/of_address.h
index 66117b1fa7f8..4e5faf6f7783 100644
--- a/include/of_address.h
+++ b/include/of_address.h
@@ -60,6 +60,8 @@ extern void __iomem *of_iomap(struct device_node *np, int index);
 extern int of_dma_get_range(struct device_node *np, u64 *dma_addr, u64 *paddr,
 			    u64 *size);
 
+extern bool of_dma_is_coherent(struct device_node *np);
+
 #else /* CONFIG_OFTREE */
 
 static inline u64 of_translate_address(struct device_node *dev,
@@ -109,6 +111,10 @@ static inline int of_dma_get_range(struct device_node *np, u64 *dma_addr,
 	return -ENOSYS;
 }
 
+static inline bool of_dma_is_coherent(struct device_node *np)
+{
+	return false;
+}
 #endif /* CONFIG_OFTREE */
 
 #ifdef CONFIG_OF_PCI
-- 
2.30.2