On Fri, Sep 06, 2002 at 01:04:28PM -0700, Matthew Dharm wrote: > So, I've got an interesting problem... which has forced me to look at > the use of the LOADADDR variable in the Makefile, and try (quickly) to > brush up on my linker scripting... > > Basically I've got a processor with on-chip registers that need to be > located in the first 512MByte of _physical_ address. To make things > difficult, they cannot be re-located once placed (configuration is > done by a hardware config stream at reset). It's only 16KBytes of > address, but since I recall that linux on mips can't (well, probably > can't) handle discontiguous memory maps (we discussed this about a > year ago, I think), I was looking for a good place to put them. > > Now, I think my problems are solved if the LOADADDR variable works the > way I think it does -- that the kernel loads at that address, and only > uses memory from that point upwards. So, if my LOADADDR is > 0x80100000, then the first 0x100000 won't get used. Of course, the > exception vectors are there, but that doesn't take up that much space. > So there should be a chunk of address space I can use for other > things, like this register bank. > > Yes? No? Is my understanding even close? > That is right. The only catch is that if you make LOADADDR very high (as in the case system ram starts at a high address), the kernel page table will be very high too. It starts from phys address 0. Also if you map your control registers at near-zero phy address, don't you also have system RAM there too? Normally it is not ok to have two devices decoded at the same phys address. > P.S. Of course, if this is right, then I need to figure out the > proper/best way to use the add_memory_region() function.... Unless I misunderstand something here, I don't think you need to mess with add_memory_region(). Jun
