This is an attempt to document the endian field in memory API. As this is a confusing topic, it's best to make the text as explicit as possible.
Signed-off-by: Michael S. Tsirkin <m...@redhat.com> --- docs/memory.txt | 28 ++++++++++++++++++++++++++++ 1 files changed, 28 insertions(+), 0 deletions(-) diff --git a/docs/memory.txt b/docs/memory.txt index 5bbee8e..ff92b52 100644 --- a/docs/memory.txt +++ b/docs/memory.txt @@ -170,3 +170,31 @@ various constraints can be supplied to control how these callbacks are called: - .old_portio and .old_mmio can be used to ease porting from code using cpu_register_io_memory() and register_ioport(). They should not be used in new code. +- .endianness; specifies the device endian-ness, which affects + the value parameter passed from guest to write and returned + to guest from read callbacks, as follows: + void write(void *opaque, target_phys_addr_t addr, + uint64_t value, unsigned size) + uint64_t read(void *opaque, target_phys_addr_t addr, + unsigned size) + Legal values are: + DEVICE_NATIVE_ENDIAN - Callbacks accept and return value in + host endian format. This makes it possible to do + math on values without type conversions. + Low size bytes in value are set, the rest are zero padded + on input and ignored on output. + DEVICE_LITTLE_ENDIAN - Callbacks accept and return value + in little endian format. This is appropriate + if you need to directly copy the data into device memory, + and the device programming interface is little endian + (true for most pci devices). + First size bytes in value are set, the rest are zero padded + on input and ignored on output. + DEVICE_BIG_ENDIAN - Callbacks accept and return value + in big endian format. + in little endian format. This is appropriate + if you need to directly copy the data into device memory, + and the device programming interface is big endian + (true e.g. for some system devices on big endian architectures). + Last size bytes in value are set, the rest are zero padded + on input and ignored on output. -- 1.7.9.111.gf3fb0