This implements the 'nonposted-mmio' boolean property. Placing this
property in a bus marks all direct child devices as requiring
non-posted MMIO mappings. If no such property is found, the default
is posted MMIO.

of_mmio_is_nonposted() performs this check to determine if a given
device has requested non-posted MMIO.

of_address_to_resource() uses this to set the IORESOURCE_MEM_NONPOSTED
flag on resources that require non-posted MMIO.

of_iomap() and of_io_request_and_map() then use this flag to pick the
correct ioremap() variant.

This mechanism is currently restricted to builds that support Apple ARM
platforms, as an optimization.

Reviewed-by: Linus Walleij <redacted>
Signed-off-by: Hector Martin <redacted>
---
 drivers/of/address.c       | 43 ++++++++++++++++++++++++++++++++++++--
 include/linux/of_address.h |  1 +
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/drivers/of/address.c b/drivers/of/address.c
index 73ddf2540f3f..6485cc536e81 100644
--- a/drivers/of/address.c
+++ b/drivers/of/address.c

@@ -847,6 +847,9 @@ static int __of_address_to_resource(struct device_node *dev,
 		return -EINVAL;
 	memset(r, 0, sizeof(struct resource));
 
+	if (of_mmio_is_nonposted(dev))
+		flags |= IORESOURCE_MEM_NONPOSTED;
+
 	r->start = taddr;
 	r->end = taddr + size - 1;
 	r->flags = flags;

@@ -896,7 +899,10 @@ void __iomem *of_iomap(struct device_node *np, int index)
 	if (of_address_to_resource(np, index, &res))
 		return NULL;
 
-	return ioremap(res.start, resource_size(&res));
+	if (res.flags & IORESOURCE_MEM_NONPOSTED)
+		return ioremap_np(res.start, resource_size(&res));
+	else
+		return ioremap(res.start, resource_size(&res));
 }
 EXPORT_SYMBOL(of_iomap);
 

@@ -928,7 +934,11 @@ void __iomem *of_io_request_and_map(struct device_node *np, int index,
 	if (!request_mem_region(res.start, resource_size(&res), name))
 		return IOMEM_ERR_PTR(-EBUSY);
 
-	mem = ioremap(res.start, resource_size(&res));
+	if (res.flags & IORESOURCE_MEM_NONPOSTED)
+		mem = ioremap_np(res.start, resource_size(&res));
+	else
+		mem = ioremap(res.start, resource_size(&res));
+
 	if (!mem) {
 		release_mem_region(res.start, resource_size(&res));
 		return IOMEM_ERR_PTR(-ENOMEM);

@@ -1094,3 +1104,32 @@ bool of_dma_is_coherent(struct device_node *np)
 	return false;
 }
 EXPORT_SYMBOL_GPL(of_dma_is_coherent);
+
+/**
+ * of_mmio_is_nonposted - Check if device uses non-posted MMIO
+ * @np:	device node
+ *
+ * Returns true if the "nonposted-mmio" property was found for
+ * the device's bus.
+ *
+ * This is currently only enabled on builds that support Apple ARM devices, as
+ * an optimization.
+ */
+bool of_mmio_is_nonposted(struct device_node *np)
+{
+	struct device_node *parent;
+	bool nonposted;
+
+	if (!IS_ENABLED(CONFIG_ARCH_APPLE))
+		return false;
+
+	parent = of_get_parent(np);
+	if (!parent)
+		return false;
+
+	nonposted = of_property_read_bool(parent, "nonposted-mmio");
+
+	of_node_put(parent);
+	return nonposted;
+}
+EXPORT_SYMBOL_GPL(of_mmio_is_nonposted);