Commit 37786c7f authored by Kevin Cernekee's avatar Kevin Cernekee Committed by Rob Herring
Browse files

of: Add helper function to check MMIO register endianness

SoC peripherals can come in several different flavors:

 - little-endian: registers always need to be accessed in LE mode (so the
   kernel should perform a swap if the CPU is running BE)

 - big-endian: registers always need to be accessed in BE mode (so the
   kernel should perform a swap if the CPU is running LE)

 - native-endian: the bus will automatically swap accesses, so the kernel
   should never swap

Introduce a function that checks an OF device node to see whether it
contains a "big-endian" or "native-endian" property.  For the former case,
always return true.  For the latter case, return true iff the kernel was
built for BE (implying that the BE MMIO accessors do not perform a swap).
Otherwise return false, assuming LE registers.

LE registers are assumed by default because most existing drivers (libahci,
serial8250, usb) always use readl/writel in the absence of instructions
to the contrary, so that will be our fallback.
Signed-off-by: default avatarKevin Cernekee <>
Reviewed-by: default avatarPeter Hurley <>
Acked-by: default avatarGreg Kroah-Hartman <>
Signed-off-by: default avatarRob Herring <>
parent c954b36e
......@@ -567,6 +567,29 @@ bool of_device_is_available(const struct device_node *device)
* of_device_is_big_endian - check if a device has BE registers
* @device: Node to check for endianness
* Returns true if the device has a "big-endian" property, or if the kernel
* was compiled for BE *and* the device has a "native-endian" property.
* Returns false otherwise.
* Callers would nominally use ioread32be/iowrite32be if
* of_device_is_big_endian() == true, or readl/writel otherwise.
bool of_device_is_big_endian(const struct device_node *device)
if (of_property_read_bool(device, "big-endian"))
return true;
of_property_read_bool(device, "native-endian"))
return true;
return false;
* of_get_parent - Get a node's parent if any
* @node: Node to get parent
......@@ -305,6 +305,7 @@ extern int of_property_read_string_helper(struct device_node *np,
extern int of_device_is_compatible(const struct device_node *device,
const char *);
extern bool of_device_is_available(const struct device_node *device);
extern bool of_device_is_big_endian(const struct device_node *device);
extern const void *of_get_property(const struct device_node *node,
const char *name,
int *lenp);
......@@ -466,6 +467,11 @@ static inline bool of_device_is_available(const struct device_node *device)
return false;
static inline bool of_device_is_big_endian(const struct device_node *device)
return false;
static inline struct property *of_find_property(const struct device_node *np,
const char *name,
int *lenp)
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