From 37786c7fee40771d13901de129af7e084ed48b55 Mon Sep 17 00:00:00 2001 From: Kevin Cernekee Date: Thu, 9 Apr 2015 13:05:14 -0700 Subject: [PATCH] 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: Kevin Cernekee Reviewed-by: Peter Hurley Acked-by: Greg Kroah-Hartman Signed-off-by: Rob Herring --- drivers/of/base.c | 23 +++++++++++++++++++++++ include/linux/of.h | 6 ++++++ 2 files changed, 29 insertions(+) diff --git a/drivers/of/base.c b/drivers/of/base.c index 69566b6a876d..31ca3c8dae61 100644 --- a/drivers/of/base.c +++ b/drivers/of/base.c @@ -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 diff --git a/include/linux/of.h b/include/linux/of.h index dfde07e77a63..a0cd62ef22db 100644 --- a/include/linux/of.h +++ b/include/linux/of.h @@ -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) -- 2.20.1