[PATCH RFC 09/12] of: populate new device_d::dma_coherent attribute

[Ahmad Fatoum]

So far, whether device DMA is coherent was a one-time global decision.
This is insufficient, because some platforms:

 - are cache coherent, while the architecture isn't in general, e.g. ARM
   with CONFIG_MMU=y assumes non-coherent DMA, but LS1046A is coherent

 - have a mix of devices that snoop caches and devices that don't
   (StarFive JH7100).

To enable dev_dma_(map|unmap)_single to take the correct device-specific
action with regards to cache maintenance, provide dev_is_dma_coherent()
with semantics similar to what Linux provides.

This admittedly looks a bit ugly, but we will refrain from making
dma_coherent defined independent of ifdef CONFIG_ARCH_HAS_NONCOHERENT_DMA:
On platforms that are cache-coherent, we will want dev->dma_coherent to
be true. Yet not all code allocating devices uses dev_alloc(), so adding
a global toggle is a bit too much refactoring effort for now.

Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
 commands/devinfo.c    |  5 +++++
 drivers/of/platform.c |  3 +++
 include/driver.h      | 28 ++++++++++++++++++++++++++++
 3 files changed, 36 insertions(+)

diff --git a/commands/devinfo.c b/commands/devinfo.c
index 2487786c7101..be28d02028c3 100644
--- a/commands/devinfo.c
+++ b/commands/devinfo.c
@@ -50,6 +50,7 @@ static int do_devinfo(int argc, char *argv[])
 	struct param_d *param;
 	int i;
 	int first;
+	int coherent;
 	struct resource *res;
 
 	if (argc == 1) {
@@ -82,6 +83,10 @@ static int do_devinfo(int argc, char *argv[])
 		if (dev->bus)
 			printf("Bus: %s\n", dev->bus->name);
 
+		coherent = dev_is_dma_coherent(dev);
+		if (coherent >= 0)
+			printf("DMA Coherent: %s\n", coherent ? "true" : "false");
+
 		if (dev->info)
 			dev->info(dev);
 
diff --git a/drivers/of/platform.c b/drivers/of/platform.c
index 0982873446a6..1bd5d41ba226 100644
--- a/drivers/of/platform.c
+++ b/drivers/of/platform.c
@@ -128,6 +128,9 @@ static void of_dma_configure(struct device *dev, struct device_node *np)
 	}
 
 	dev->dma_offset = offset;
+#ifdef CONFIG_OF_DMA_COHERENCY
+	dev->dma_coherent = of_dma_is_coherent(np);
+#endif
 }
 
 /**
diff --git a/include/driver.h b/include/driver.h
index 7e25c060280b..f6301d954bb5 100644
--- a/include/driver.h
+++ b/include/driver.h
@@ -8,6 +8,7 @@
 
 #include <linux/list.h>
 #include <linux/ioport.h>
+#include <linux/bitops.h>
 #include <of.h>
 #include <filetype.h>
 
@@ -43,6 +44,13 @@ struct device {
 	 * something like eth0 or nor0. */
 	int id;
 
+	/*! This particular device is dma coherent, even if the
+         * architecture supports non-coherent devices.
+	 */
+#ifdef CONFIG_OF_DMA_COHERENCY
+	bool dma_coherent:1;
+#endif
+
 	struct resource *resource;
 	int num_resources;
 
@@ -652,6 +660,26 @@ static inline struct device_node *dev_of_node(struct device *dev)
 	return IS_ENABLED(CONFIG_OFDEVICE) ? dev->of_node : NULL;
 }
 
+#ifdef CONFIG_OF_DMA_COHERENCY
+static inline int __dev_is_dma_coherent(struct device *dev)
+{
+	return dev->dma_coherent;
+}
+#else
+static inline bool __dev_is_dma_coherent(struct device *dev)
+{
+	return IS_ENABLED(CONFIG_OF_DMA_DEFAULT_COHERENT);
+}
+#endif
+
+static inline int dev_is_dma_coherent(struct device *dev)
+{
+	if (!dev_of_node(dev))
+		return -EINVAL;
+
+	return __dev_is_dma_coherent(dev);
+}
+
 static inline void *dev_get_priv(const struct device *dev)
 {
 	return dev->priv;
-- 
2.30.2