On Thu, 2009-07-09 at 20:15 -0400, John David Anglin wrote: > > On Thu, Jul 09, 2009 at 03:11:19PM +0200, Artem Alimarine wrote: > > > Hi guys, > > > > > > I am new to PARISC and to this forum. I have a small question. There is > > > an instruction in entry.S that I do not understand. It is in the the > > > macro make_insert_tlb > > > > > > Kernel 2.6.26.2: > > > > > > 537 /* Enforce uncacheable pages. > > > 538 * This should ONLY be use for MMIO on PA 2.0 machines. > > > 539 * Memory/DMA is cache coherent on all PA2.0 machines we support > > > 540 * (that means T-class is NOT supported) and the memory controllers > > > 541 * on most of those machines only handles cache transactions. > > > 542 */ > > > 543 extrd,u,*= \pte,_PAGE_NO_CACHE_BIT+32,1,%r0 > > > 544 depi 1,12,1,\prot > > > > > > > > > > The "*=" in line 543 will determine if "depi" instruction (line 544) > > gets executed or not. You'll need the "PA-RISC 2.0 Architecture": > > http://www.parisc-linux.org/documentation/index.html > > http://ftp.parisc-linux.org/docs/arch/parisc2.0.pdf > > > > And read page 7-47, 7-48, and Table D-14. > > > > > > > The DEPI instruction on a 64-bit machine sets bit 44=32+12, > > > whereas we use the value as the argument to IDTLBT, which expects bit 12 > > > to be used instead. > > > > > > Does it mean that the U-bit is never set and the > > > authorization id gets corrupted??? > > > > U-bit will get set only if _PAGE_NO_CACHE_BIT+32 is also set. > > > > The bit enumeration is *reverse* with MSb being 0 for all ASM instructions > > and all references in the PA2.0 Arch manual. > > > > Because this is a 64 bit build, "+32" is needed to refer to the lower half > > of the double word (word == 32 bits). > > > > > Is it a bug or my misunderstanding of the code??? > > > > It looks correct to me. "12" here always seems to refer to the U-bit as > > defined in the PA2.0 Arch manual. > > To me, it looks like the instruction should be a depdi. See the preceding > deposit of PAGE_USER. According to the IDTLBT description, the U bit is > bit 12 in r2, not bit 44. > > rp3440 boots with the depdi change. Building gcc... Yes, looks like we've got a set of cockups in this file. Apparently gas is evaluating depi as the macro DEPI, which seems to be correct for every other case in the file I've looked at except this one. I suppose the whole file needs fixing ... preferably with a macro whose name isn't an instruction mnemonic. James -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
