> 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... Dave -- J. David Anglin dave.anglin@xxxxxxxxxxxxxx National Research Council of Canada (613) 990-0752 (FAX: 952-6602) -- 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
