Re: ask two question about e500 implementation in arch/ppc/kernel/head_fsl_booke.S

On Jul 11, 2007, at 5:21 AM, kang shuo wrote:

hi,galak:
             I have two question about e500 part of linux kernel. I
can not get reponse from maillist . So I sent the questions to you
directly.

1. in  arch/ppc/kernel/head_fsl_booke.S
603         FIND_PTE
604         andi.   r13, r11, _PAGE_PRESENT /* Is the page present? */
605         beq     2f                      /* Bail if not present */

That seems _PAGE_PRESENT should be set before enter DataTLBError
exception handler(Or the following finish_tlb_load function will not
execute), but  in __ioremap function of e500 implementation,
_PAGE_PRESENT bit is not set for an io address map.Why?

_PAGE_PRESENT is sent when we use the page not when we map it.  So on  
the first fault we set _PAGE_PRESENT.

2. still in   arch/ppc/kernel/head_fsl_booke.S
791 #ifdef CONFIG_E200
792         /* Round robin TLB1 entries assignment */
793         mfspr   r12, SPRN_MAS0
794
795         /* Extract TLB1CFG(NENTRY) */
796         mfspr   r11, SPRN_TLB1CFG
797         andi.   r11, r11, 0xfff
798
799         /* Extract MAS0(NV) */
800         andi.   r13, r12, 0xfff
801         addi    r13, r13, 1
802         cmpw    0, r13, r11
803         addi    r12, r12, 1
804
805         /* check if we need to wrap */
806         blt     7f
807
808         /* wrap back to first free tlbcam entry */
809         lis     r13, tlbcam_index@ha
810         lwz     r13, tlbcam_index@l(r13)
811         rlwimi  r12, r13, 0, 20, 31
812 7:
813         mtspr   SPRN_MAS0,r12
814 #endif /* CONFIG_E200 */
815
816         tlbwe

That seems original tlb entry will be overwritten in the above code
for e500? Why , I thought a free tlb entry should be select and fill
for e500. Just like CONFIG_E200.

Huh? The above code is for E200 only.  Maybe the issue you're missing  
is that on E500 the NV bit is updated by HW.

- k