On Fri, 25 Jul 2003, Eugene Surovegin wrote: > At 12:22 PM 7/25/2003, Wolfgang Denk wrote: > > > accessed through a structure? Is it acceptable to do: > > > > > > #define MYHW (MY_MBAR+42) > > > > > > ... > > > > > > out_be32(MYHW, 0xco1df00d); > > > >...I would not accept such code. > > > >There is one fundamental difference: a field in a struct has a type, > >i. e. the compiler "knows" how big it is (8, 16, 32, ... bits), if > >special attributes apply (volatile), etc. > > Although functions like out_be32 also *know* the size :). > > IMHO, it's not a good idea to access IO remmaped registers simply through C > struct, it's better and safe to use out_* and in_*.
Wouldn't best practices also include using a base address rather than a constant, so that when a new board places the hardware in a different location all you have to do is find it? out_be32(my_bar + offsetof(myregs_t, sna_reg), 0xdeadbeef); > There are issues that C struct cannot deal with - load/store reodering (of > course you can insert wmb() and friends if you know what you are doing :). > > I think the best practice is to use C struct (for readability) and > out_*/in_* on structure members for actual access. I've always written low level I/O routines for everything in a driver because it is easier to adapt when someone changes how they want to do access to the device. The code all calls the low level IO routines. -Bret -- Bret Indrelee QLogic Corporation Bret.Indrelee at qlogic.com 6321 Bury Drive, St 13, Eden Prairie, MN 55346 ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
