On Tue, Jul 22, 2003 at 09:39:40PM +0200, Maciej W. Rozycki wrote: > > sparc32 and sparc64 processors and systems are significantly > > different. For example, the SRMMU present in v8 CPUs is 100% replaced > > with a totally different MMU (indeed, totally different instructions, > > access methods, etc) in v9. Accordingly there is very little code in > > common between the two ports, and most of that is in device handling; > > code that is in drivers/sbus and thus shared anyway. > > Well, the MMU of (original) 32-bit MIPS processors (i.e. R2k/R3k) is > completely different from the one in later ones, too. I suspect this is > true for the R6k as well. The exception handlers differ a bit as well, > especially considering the XTLB refill one. That probably counts as > nitpicking, though... It's also a question of taste - and that one can be discussed forever. How far do you want to factor our common code, as little as possible which was our previous approach or extremly aggressive, glibc-like. And yes, the R6000 is different. With that in mind R2000 and R4000 look like enzygotic twins ... > > Something that made sense for sparc might not make sense for mips. > > Certainly it needs to be analysed on a case by case basis, avoiding > blanket assumptions. Anyway, I still see two reasons for having at least > a separate top-level directory: > > 1. A better separation of the more straightforward 32-bit Makefile and the > more complicated 64-bit one. > > 2. A better visual existence of the 64-bit port; not really a technical > advantage, but more a psychological one. It stops any newcomer wondering > whether we support 64-bit systems natively or not. I was thinking about that also. arch/mips64 and include/asm-mips64 will go away but on the other side there will be an option to configure a 64-bit kernel in the menus - which will hopefully be more visible than just two subdirectories. > There is also no point in having headers in asm-mips consisting of a > single #ifdef CONFIG_MIPS32/#else/#endif conditional, where two distinct > versions should be present in asm-mips and asm-mips64, respectively. It's > easier to make a diff between such separate implementations to verify > everything's OK. Like 80% of the headers could be identical between both files without lots of trickery. The current approach is have two physical copies of these identical files. Btw, an old experience repeats - some of the code was identical except inline assembler using addu etc. for 32-bit and daddu etc. for 64-bit. I rewrote that stuff to use C for this arithmetic. The result - less inline assembler, more readable code and a file that's identical for both 32-bit and 64-bit. Ralf
