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of: Add helper function to check MMIO register endianness

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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: Kevin Cernekee <cernekee@gmail.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Rob Herring <robh@kernel.org>
This commit is contained in:
Kevin Cernekee
2015-04-09 13:05:14 -07:00
committed by Rob Herring
parent c954b36e3f
commit 37786c7fee
2 changed files with 29 additions and 0 deletions
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6
include/linux/of.h
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@@ -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)