Hi Daniel, Em Mon, 14 Sep 2020 12:14:38 -0300 "Daniel W. S. Almeida" <dwlsalme...@gmail.com> escreveu:
> Hi Mauro, > > > Genmask is always highest order to low order. It doesn't make > > any sense to make it depends on endiannes. > > > > I added these #ifdefs due to this: > > https://lwn.net/Articles/741762/ > > i.e. > > Fields to access are specified as GENMASK() values - an N-bit field > starting at bit #M is encoded as GENMASK(M + N - 1, N). Note that > bit numbers refer to endianness of the object we are working with - > e.g. GENMASK(11, 0) in __be16 refers to the second byte and the lower > 4 bits of the first byte. In __le16 it would refer to the first byte > and the lower 4 bits of the second byte, etc. > > I am not 100% sure, but maybe we actually need them? By looking at the changes you did with regards to bitfields, it sounds that you didn't quite get how BE/LE works. Basically, if the CPU needs to store a value (like 0x8001) on some place, it will store two values: 0x80 and 0x01. Depending on the endiannes, either 0x80 or 0x01 will be stored first. See: https://en.wikipedia.org/wiki/Endianness In any case, when you do something like: mask = GENMASK(11, 0); ret = be16_to_cpu(s->bitfield) & mask; The be16_to_cpu() will ensure that the bits will be at the position expected by the CPU endiannes. So, no need to check for __BIG_ENDIAN or __LITTLE_ENDIAN when be*_to_cpu() macros are used. Please also notice that, when there's just one byte to be stored (e. g. 8 bits), the endiannes won't matter, as the bits will still be stored at the same way. that's why there's no be8_to_cpu() or cpu_to_be8() macros. Thanks, Mauro
