I have investigated a little further, and in arch/ppc/mm/init.c, it calls ppc_md.setup_io_mapping(), which remaps 1:1 the BCSRs (in arch/ppc/kernel/m8xx_map_io), so (if I understand your explanation and the code properly) the BCSR should be at the same address in PPCBOOT and in the kernel space... so accessing offset ff010000 in /dev/mem or /dev/kmem should give me access to it... is that it ? Because if it is, I can't make it work...
I'll try to access some of the internal maps in the IMMR to see if they work... thx anyway Jeremy >>> Magnus Damm <damm at opensource.se> 03/04/02 10:57am >>> Hi, If you have memory-mapped io (The (F)ADS8xx BCSR registers is a good example) which is mapped to a certain physical address, it is very simple to access it if the MMU is turned off. The Linux kernel runs with the MMU on, and it needs a virtual-to-physical address mapping to be able to access memory-mapped io. So, my 2.2-kernel has a file called arch/ppc/mm/init.c. Inside that file there's a function called "ioremap()" - that is what you are looking for. Make sure that your Linux kernel has a virtual page for your io-area, and access the virtual address that is returned by "ioremap()". If you use "ioremap()" before a certain moment when the Linux kernel starts up, you will get a 1:1 mapping between virtual and physical addresses. (This is true for 2.2 anyhow) Look how the internal io block is ioremap():ped for a good example how it is done. Cheers / magnus Jeremy Rosen wrote: > > Hello everybody, > > I have 860T FADS board, and I am trying to access the (board specific) > registers BCSRs. > > I have no problem accessing them in PPCBOOT, since they are accessed > through CS1, at address FF01xxxx, but I can't access them in linux for > the moment. > My first attempt was by using the /dev/mem device, but it doesn't seem > to work, the result read are not correct. > so I have to question > 1) why doesn't it work, I probably don't understand how /dev/mem works > : does it map only memory and not the address space ? do I have to > register the address range or the BCSR in the kernel ? > 2) what is the proper way of doing this ? writing a driver ? or using > /dev/mem properly ? > > thx for your help... > > Jeremy > ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
