Hennerich, Michael wrote: > >> Wolfgang Grandegger wrote: >>> Mike Frysinger wrote: >>>> On Thu, Dec 10, 2009 at 04:11, Wolfgang Grandegger wrote: >>>>> Barry Song wrote: >>>>>> +#include <linux/module.h> >>>>>> +#include <linux/init.h> >>>>>> +#include <linux/kernel.h> >>>>>> +#include <linux/types.h> >>>>> I think you don't need "types.h" as the code no longer uses >> "uint*_t". >>>> linux/types.h declares all types, like u* which this driver still >> uses >>> I just remember that "linux/types.h" needs to be added for the > uint*_t >>> types. At a first glance I do not see __u8/u8 being defined in that >>> header file but I might have missed something. >>> >>>>> Well, I'm still not a friend of the following inline functions, >>>>> especially the *one-liners* which are called just *once*. With the >> usage >>>>> of structs they seem even more useless. >>>> seems like it would make more sense to not even use the read/write >>>> functions either. just declare the regs as volatile and assign/read >>>> the struct directly. >>> Two times no. Don't use volatile and proper accessor functions. See: >>> >>> http://lxr.linux.no/#linux+v2.6.32/Documentation/volatile-considered- >> harmful.txt >> >> I was just wondering if bfin_read/write16 would not be the proper >> accessor functions. readw/writew seems to be implemented differently: >> >> http://lxr.linux.no/#linux+v2.6.32/arch/blackfin/include/asm/io.h#L44 >> >> Puh, they do an cli,nop,nop,sync..sti for the access. This also nicely >> shows why accessor functions should be used to access device registers. >> >> Well, just curious. I don't really know the blackfin arch. > > Well - on Blackfin its absolutely ok to access System Memory Mapped > Registers using structs. > At any rate volatile is then required to prevent the compiler to > optimize accesses away. > IMHO this is a pretty legal use of volatile, and used in hundreds of > places all over the kernel. > > When accessing external controllers accessor functions from io.h must be > used. > There are two things to consider here: > 1) weak ordering of reads and writes > 2) killed and reissued reads (especially harmful when reading from > FIFOs)
OK, anyway, I believe that it's good practice to hide all such details by using proper accessor functions. Wolfgang. _______________________________________________ Socketcan-core mailing list [email protected] https://lists.berlios.de/mailman/listinfo/socketcan-core
