On Tue, Nov 17, 2009 at 04:12:03PM +0800, figo zhang wrote: > hi, all, > i have a qusetion , in arch/mips/mm/tlb-r4k.c, __update_tlb() function: > 321<http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=arch/mips/mm/tlb-r4k.c;h=d73428b18b0a41da13e81c64021e62505200ff2d;hb=317c68c04d53198f38314d29ba28b8fc632eccab#l321>#if > defined(CONFIG_64BIT_PHYS_ADDR) && defined(CONFIG_CPU_MIPS32) > 322<http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=arch/mips/mm/tlb-r4k.c;h=d73428b18b0a41da13e81c64021e62505200ff2d;hb=317c68c04d53198f38314d29ba28b8fc632eccab#l322> > write_c0_entrylo0(ptep->pte_high); > 323<http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=arch/mips/mm/tlb-r4k.c;h=d73428b18b0a41da13e81c64021e62505200ff2d;hb=317c68c04d53198f38314d29ba28b8fc632eccab#l323> > ptep++; > 324<http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=arch/mips/mm/tlb-r4k.c;h=d73428b18b0a41da13e81c64021e62505200ff2d;hb=317c68c04d53198f38314d29ba28b8fc632eccab#l324> > write_c0_entrylo1(ptep->pte_high); > 325<http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=arch/mips/mm/tlb-r4k.c;h=d73428b18b0a41da13e81c64021e62505200ff2d;hb=317c68c04d53198f38314d29ba28b8fc632eccab#l325>#else > 326<http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=arch/mips/mm/tlb-r4k.c;h=d73428b18b0a41da13e81c64021e62505200ff2d;hb=317c68c04d53198f38314d29ba28b8fc632eccab#l326> > write_c0_entrylo0(pte_val(*ptep++) >> 6); > 327<http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=arch/mips/mm/tlb-r4k.c;h=d73428b18b0a41da13e81c64021e62505200ff2d;hb=317c68c04d53198f38314d29ba28b8fc632eccab#l327> > write_c0_entrylo1(pte_val(*ptep) >> 6); > 328<http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=arch/mips/mm/tlb-r4k.c;h=d73428b18b0a41da13e81c64021e62505200ff2d;hb=317c68c04d53198f38314d29ba28b8fc632eccab#l328>#endif > > why this right shift 6 bits? this 6 bits contain some important bit, such > as: > C: [bit3~5]: cohereny attribute of page No, the low 6 bits contain other information maintained by the kernel. Shifting right by 6 bits is used to drop these software bits. The hardware bits are stored in bits 6 and up in a pte so the shift operation is going to move them into the right place. > D: > V: > G: > > and how the kernel write the this 6 bit to entrylo0/1 register? A TLB write instruction about 5 lines further down in the code. Ralf
