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 <cernekee@gmail.com>
Reviewed-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarRob Herring <robh@kernel.org>
parent c954b36e

drivers/of/base.c

+23 −0
Original line number Diff line number Diff line
@@ -567,6 +567,29 @@ bool of_device_is_available(const struct device_node *device) 
}

EXPORT_SYMBOL(of_device_is_available);



/**

 *  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;

	if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN) &&

	    of_property_read_bool(device, "native-endian"))

		return true;

	return false;

}

EXPORT_SYMBOL(of_device_is_big_endian);



/**

 *	of_get_parent - Get a node's parent if any

 *	@node:	Node to get parent

include/linux/of.h

+6 −0
Original line number Diff line number Diff line
@@ -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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