Messages in this thread | | | Date | Tue, 21 Dec 1999 18:48:18 -0500 | From | "Theodore Y. Ts'o" <> | Subject | Re: [patch] read[bwl] and ioremap problem |
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Date: Sat, 18 Dec 1999 15:50:19 -0800 (PST) From: Linus Torvalds <torvalds@transmeta.com>
THAT case is certainly a rather strong argument for using something like "gsc_read[bwl]()" on HP-PA.
The other strong reason for doing gsc_read[bwl] on HP-PA is that some PA-RISC boxes have both a GSC bus *and* a PCI bus, and you need to access devices on both buses....
Something to consider is that for certain drivers, such as the serial driver, I'm already having to do a serial_inp() which dispatches to the proper {inb,readb,gsc_readb} already. Yes I take a overhead/performance hit for doing this, but it's the only clean way to support both ISA and PCI serial boards in a single i386 box, or to support multiple buses in the HP-PA scenario.
We've historically said that this kind of thing is horrible for performance reasons, and the SCO and NetBSD approaches of doing parameterized I/O has been derided for that reason. However, it's something that perhaps we should rethink; on modern CPU's, the extra procedure activation/deactivation isn't *that* expensive, and it ends up making the drivers much more portable and easier to support multiple architectures. The alternative is that each driver author ends up writing their own I/O dispatch routines, such as what's currently in the serial driver. While this approach does have some advantages, in that each driver author can decide whether or not he/she wishes to pay the indirection overhead, it can mean code duplication and a delay before certain devices get supported on non-mainline architectures.
Something to think about.
- Ted
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