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: > > Actually there still have one limitation that we have to make sure > > that the kernel and dtb are in the 64M memory mapped by the init tlb entry. > > I booted the kernel successfully by using the following u-boot commands: > > setenv fdt_high 0xffffffff > > dhcp 6000000 128.224.162.196:/vlm-boards/p5020/uImage > > tftp 6f00000 128.224.162.196:/vlm-boards/p5020/p5020ds.dtb > > bootm 6000000 - 6f00000 > > > > > > OK, that was it -- I hadn't set fdt_high and thus U-Boot was relocating > the fdt under 64M. > > We should probably be using ioremap_prot() (or some other mechanism) to
It is too early to use ioremap_prot() for this case. > create a special mapping, rather than assuming the fdt is covered by the > initial TLB entry. That doesn't need to happen as part of this > patchset, of course, as it's not a new limitation. In order to fix this limitation we would have to create a separate map for the dtb if it is not covered by the init 64M tlb. I would like to give it a try if I can get some time. > > > > 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". :-) > > 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. Thanks, Kevin > > If you're OK with these changes, I can fix it while applying. > > -Scott > >
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