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 <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>
2 files changed