On Wed, 2014-01-08 at 10:42 +0800, Kevin Hao wrote: > On Tue, Jan 07, 2014 at 05:46:04PM -0600, Scott Wood wrote: > > On Sat, 2014-01-04 at 14:34 +0800, Kevin Hao wrote: > > > > I'm having a hard time following the logic here. What is PAGE_OFFSET - > > > > offset supposed to be? Why would we map anything belowe PAGE_OFFSET? > > > > > > No, we don't map the address below PAGE_OFFSET. > > > memstart_addr is the physical start address of RAM. > > > start is the kernel running physical address aligned with 64M. > > > > > > offset = memstart_addr - start > > > > > > So if memstart_addr < start, the offset is negative. The PAGE_OFFSET - > > > offset > > > is the virtual start address we should use for the init 64M map. It's > > > above > > > the PAGE_OFFSET instead of below. > > > > Oh. I think it'd be more readable to do "offset = start - > > memstart_addr" and add offset instead of subtracting it. > > Yes, I agree. The reason that I use "offset = memstart_addr - start" is that > it seems "memstart_addr" is always greater than "start" when we are booting > a kdump kernel with a kernel option like "crashkernel=64M@80M". :-)
...so there is a situation where you map below PAGE_OFFSET. :-) > > Also, offset should be phys_addr_t -- even if you don't expect to > > support offsets greater than 4G on 32-bit, it's semantically the right > > type to use. Plus, "int" would break if this code were ever used with > > 64-bit. > > I thought about using phy_addr_t for the "offset" originally but gave it up > for the following reasons: > * It will not be greater than 4G. > * We have to use the ugly #ifdef CONFIG_PHYS_64BIT in restore_to_as0(). > * Need more registers for arguments for restore_to_as0(). > > Of course you can change it to phys_addr_t if you prefer. I'd at least like to make it "long". -Scott _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
