On Oct 5, 2012, at 10:08 AM, John Baldwin wrote: > On Thursday, October 04, 2012 1:20:52 pm Carl Delsey wrote: >> I noticed that the bus_space_*_8 functions are unimplemented for x86. >> Looking at the code, it seems this is intentional. >> >> Is this done because on 32-bit systems we don't know, in the general >> case, whether to read the upper or lower 32-bits first? >> >> If that's the reason, I was thinking we could provide two >> implementations for i386: bus_space_read_8_upper_first and >> bus_space_read_8_lower_first. For amd64 we would just have bus_space_read_8 >> >> Anybody who wants to use bus_space_read_8 in their file would do >> something like: >> #define BUS_SPACE_8_BYTES LOWER_FIRST >> or >> #define BUS_SPACE_8_BYTES UPPER_FIRST >> whichever is appropriate for their hardware. >> >> This would go in their source file before including bus.h and we would >> take care of mapping to the correct implementation. >> >> With the prevalence of 64-bit registers these days, if we don't provide >> an implementation, I expect many drivers will end up rolling their own. >> >> If this seems like a good idea, I'll happily whip up a patch and submit it. > > I think cxgb* already have an implementation. For amd64 we should certainly > have bus_space_*_8(), at least for SYS_RES_MEMORY. I think they should fail > for SYS_RES_IOPORT. I don't think we can force a compile-time error though, > would just have to return -1 on reads or some such?
I believe it was because bus reads weren't guaranteed to be atomic on i386. don't know if that's still the case or a concern, but it was an intentional omission. Warner _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "freebsd-hackers-unsubscr...@freebsd.org"
