On Tue, Jul 02, 2013 at 05:41:05PM -0500, Scott Wood wrote:
> On 07/01/2013 10:45:14 PM, Kevin Hao wrote:
> >On Mon, Jul 01, 2013 at 08:00:06PM -0500, Scott Wood wrote:
> >> On 06/30/2013 02:35:21 AM, Kevin Hao wrote:
> >> >On Thu, Jun 27, 2013 at 09:19:06PM -0500, Scott Wood wrote:
> >> >> On 06/26/2013 09:00:34 PM, Kevin Hao wrote:
> >> >> >diff --git a/arch/powerpc/include/asm/mmu-book3e.h
> >> >> >b/arch/powerpc/include/asm/mmu-book3e.h
> >> >> >index 936db36..bf422db 100644
> >> >> >--- a/arch/powerpc/include/asm/mmu-book3e.h
> >> >> >+++ b/arch/powerpc/include/asm/mmu-book3e.h
> >> >> >@@ -214,6 +214,11 @@
> >> >> > #define TLBILX_T_CLASS2 6
> >> >> > #define TLBILX_T_CLASS3 7
> >> >> >
> >> >> >+#ifdef CONFIG_PPC32
> >> >> >+/* The max size that one tlb can map in a 32bit kernel. */
> >> >> >+#define PPC_PIN_SIZE (1 << 28) /* 256M */
> >> >> >+#endif
> >> >>
> >> >> That comment is not true for all chips.
> >> >
> >> >This is not for the hardware limitation.
> >>
> >> It's not for a general software limitation, either. We can use 1G
> >> mappings for user hugetlb (if the default mmap address is moved out
> >> of the way) or for the kernel lowmem mapping (if the address is
> >> moved to 0x80000000 instead of 0xc0000000).
> >>
> >> It's also possible (although unlikely at this point) that someone
> >> could make a 32-bit booke chip that cannot handle 256M mappings.
> >
> >Then I have to agree with you. :-)
> >Wish I can find a way to drop it.
>
> At least give it a comment that describes how it's actually used.
>
> >> Assuming memstart_addr isn't affected by the crashkernel reservation
> >> (if it is, could you point out where?),
> >
> >No. The memstart_addr does be affected. For example, for a boot kernel
> >with the command line with "crashkernel=32M@64M", the device tree
> >passed
> >the kdump kernel will have a memory node like this:
> > memory {
> > reg = <0x0 0x4000000 0x0 0x2000000>;
> > device_type = "memory";
> > }
> >
> >Then the memstart_addr will be set to 0x4000000 in the kdump kernel.
>
> OK, so then how does the crash kernel know which regions to dump?
> Is that indicated somewhere else in the device tree?No. We get the dump of the memory via /proc/vmcore in the kdump kernel. Thanks, Kevin > > -Scott
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