Since nobody else is replying I am giving it a shot. Hope it helps. On Tue, Dec 21, 2004 at 09:53:07AM +0100, moreau francis wrote: > Hi, > > Well, I'm still trying to port Linux on my "exotic" > board... > I hope you don't mind if I ask a couple of questions, > which may be stupid for you but usefull at my level. > If you think that linux-mips mailing list is not > intended for these kind of questions, tell me ! > > So here I am: > > I've mapped kernel code and kernel data in different > memories in order to save precious SDRAM memory. > > Code 0xC0000000 0x30000000 16Mo FLASH > Data 0xC1000000 0x20000000 8Mo SDRAM > > When running the kernel at the very begining, I > encounter different issues: > > In "tlb_init" function, cp0 WIRED register is set to > zero, therefore the call to "local_flush_tlb_all" > flush all TLB entries which were mapping my kernel > in the 3 first entries. Why is this necessary ? Setting WIRED to zero is just part of kernel start-up initialization. In 2.4 it is done before board setup routine, which allows board to setup certain wired mapping. In 2.6 it is done after board setup routine. You are screwed. :) I think this needs to be fixed. A couple of boards should be broken because of this. > In different part of the kernel it is assumed that the > kernel start at physical addr 0. For instance in > "init_bootmem" fonction, argument start is set to 0. > Or the way to calculate a page frame index in mem_map > array. Why this assumption ? > Because all other boards have phys memory starting from 0? It simplies code for sure. > Why does "mem_map" need to store page frames for > kernel > code ? mem_map holds kernel page table. Kernel code is mapped there because we start from 0 and we need to use the free memory _after_ kernel code segment. (I don't think it is very useful for MIPS though, since MIPS uses a flat 512MB block mapping for kernel virtual address.) > Are these pages going be used when the Linux is > running ? Not much in MIPS case I suppose. > I noticed CPHYSADDR macro. This macro only works if > PAGE_OFFSET is equal to 0x80000000. Why does this > macro exist ? Why not using __pa macro ? Don't know much about this one. BTW, once there was a board whose memory starts from 0x90000000. It had similar problems as yours, but I think it ran in the end. Try to search the mailing list. Jun
