Date: Wed, 10 Oct 2012 14:44:09 -0700 From: Carl Delsey <carl.r.delsey@intel.com> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-hackers@freebsd.org Subject: Re: No bus_space_read_8 on x86 ? Message-ID: <5075EC29.1010907@intel.com> In-Reply-To: <201210091154.15873.jhb@freebsd.org> References: <506DC574.9010300@intel.com> <201210051208.45550.jhb@freebsd.org> <8BC4C95F-2D10-46A5-89C8-74801BB4E23A@bsdimp.com> <201210091154.15873.jhb@freebsd.org>
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Sorry for the slow response. I was dealing with a bit of a family emergency. Responses inline below. On 10/09/12 08:54, John Baldwin wrote: > On Monday, October 08, 2012 4:59:24 pm Warner Losh wrote: >> On Oct 5, 2012, at 10:08 AM, John Baldwin wrote: <snip> >>> 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? Yes. Exactly what I was thinking. >> 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. > True. If you are on a 32-bit system you can read the two 4 byte values and > then build a 64-bit value. For 64-bit platforms we should offer bus_read_8() > however. I believe there is still no way to perform a 64-bit read on a i386 (or at least without messing with SSE instructions), but if you have to read a 64-bit register, you are stuck with doing two 32-bit reads and concatenating them. I figure we may as well provide an implementation for those who have to do that as well as the implementation for 64-bit. Anyhow, it sounds like we are basically in agreement. I'll put together a patch and send it out for review. Thanks, Carl
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