On Tue, Mar 26, 2002 at 06:35:54AM -0500, Greg Griffes wrote: > Matt, > > Thanks very much for your advice. You have saved me a big headache! > > > I really recommend using the linuxppc_2_4_devel tree as a starting > > kernel source base...but it's your choice. > > I will try using the linuxppc_2_4_devel tree. Unforeseen problems I don't > need. > > > Do you really have to map a contiguous 384MB of physical address > > space? If these are typical RTC and PIC parts...why? > > The RTC is typical but the PIC is split between a custom ASIC and > another device. The RTC is at 0xE400_0000phys, one part of the PIC > is at 0xEC00_0000phys and the other part is at 0xF700_0000phys. > Their size is small, but they are spread out. If I have to map them with > BATs, I would have to map 384Mb (because the BAT base address > must be a multiple of the mapped size.) Once the KVM is up, > I think that I can use ioremap(), or io_block_mapping() to map in > only what I need. Is that right?
You can ioremap() the devices in your board-specific *_setup_arch() routine. Early ioremap() calls start at ioremap_base and grow down. After the VM system is up, normal allocations in vmalloc space kick in. You can use io_block_mapping(), but ioremap() allows the kernel to efficiently manage your VM. Too often, people waste VM space by dropping arbitrary io_block_mappings everywhere so I would discourage it's use unless you want to utilize a BAT for specific performance/optmizations reasons in your application. > > You are misunderstanding the mapping of kernel RAM using BATs. The > > 16MB mapping is a temporary translation used before MMU_init(). > > If you look at arch/ppc/mm/ppc_mmu.c:bat_mapin_ram() you'll see > > that the final mapping is done using BAT2 and BAT3 (the third > > pair of bats is only used if total_lowmem > 256MB). > > Does this mean that before MMU_init() I can use BATs 2&3, then in > ppc_md.setup_io_mappings() (called after mapin_ram()) I would use > io_block_mapping() (as is done in chrp_setup.c?) Do you need to use the parts very early? 95% of cases don't need devices accessible within head.S. I understand anything goes with a custom board but if you are not utilizing the PIC and RTC hardware until init_IRQ() and time_init(), respectively, then you don't need to worry about early mappings via BATs. If you must use a BAT then use io_block_mapping() to accomplish it from your *_setup_arch(). If you need early access to the I/O, utilize BATs, you can utilize DBATs 2&3. Regards, -- Matt Porter MontaVista Software, Inc. mporter at mvista.com ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
