On Nov 22, 2008, at 10:01 PM, Trent Piepho wrote:
On Sat, 22 Nov 2008, Milton Miller wrote:
On Thu Nov 20 at 06:14:30 EST in 2008, Trent Piepho wrote:
- li r7,0
- lis r6,PAGE_OFFSET at h
- ori r6,r6,PAGE_OFFSET at l
- rlwimi r6,r7,0,20,31
+ lis r6,MAS2_VAL(PAGE_OFFSET, BOOKE_PAGESZ_64M,
M_IF_SMP)@h
+ ori r6,r6,MAS2_VAL(PAGE_OFFSET, BOOKE_PAGESZ_64M,
M_IF_SMP)@l
I'm fine with this part, even if the expression is a bit long. You
might
consider using LOAD_REG_IMMEDIATE from asm/ppc_asm.h to avoid
duplicating the
expression.
LOAD_REG_IMMEDIATE isn't used at all in that file, while lis/ori is
used
many times. In fact, there only one call of LOAD_REG_IMMEDIATE in
all of
arch/powerpc/kernel/*.S. So I think lis/ori is more easily
recognized.
And to be honest, I find switching syntax from assembly language
instructions to C style macros that generate instructions to be
aesthetically ugly.
It would be nice if the assembler provided a "liw" macro instruction
that
would load an immediate. When the assembler knows the immediate
value, it
could even generate shorter sequences in some cases, like when the
upper
16 bits are all zero.
I agree lis/ori is what should be used in this file and am not
interested in changing it at this point.
/* 7. Jump to KERNELBASE mapping */
- lis r6,KERNELBASE at h
- ori r6,r6,KERNELBASE at l
- rlwimi r6,r7,0,20,31
+ lis r6,(KERNELBASE & ~0xfff)@h
+ ori r6,r6,(KERNELBASE & ~0xfff)@l
Why do you need to mask off the bottom bits of KERNEL_BASE? Just
trying to
keep the instruction effect identical?
Yes, so it was clear I wasn't changing what the code did here. And to
make it clear we only wanted the page number from KERNEL_BASE. It's
an
obvious expression and a compile time constant, merely saving a few
characters in the source doesn't seem worth much. I realize it's
unnecessary since those bits get masked off in the wlwimi a few
instructions later.
Really all I wanted to fix the was memory coherency on SMP bug. But
the
code for MAS2 was stupid, so I had to change that to fix the bug in a
non-ugly way. But then r7 didn't need to be zeroed and the
(unnecessary)
"rlwimi r6,r7,0,20,31" would no longer be doing what's it's supposed
to,
so I fixed that too.
First of all, if its not aligned, then its likely other parts of
the kernel
will break. We could put a BUILD_BUG_ON somewhere (in c) if that
check is
required.
I seems like "Require KERNEL_BASE to be page aligned and modify code
to
depend on said requirement" belongs in another patch.
- addi r6,r6,24
+ addi r6,r6,(2f - 1b)
and while doing assembler math is better than the hand computed 24,
how about
doing li r9,[EMAIL PROTECTED] and just inserting that into r6? Unless you
expect step 8
to cross a page from the 1b label above. But if you are that close
to a page
boundary than assuming 1b is in the page at KERNEL_BASE would seem
to be
suspect.
For that matter, just do LOAD_ADDR(2f) or LOAD_REG_IMMEDIATE(2f),
which would
give the same result, as KERNEL_BASE should be reflected the linked
address
of the kernel (I assume that you are not doing dynamic runtime
relocation
like ppc64 on the code up to here, otherwise the previous
suggestion still
works).
I'm not sure if this code can be relocated or not. If it isn't now,
using
non-position independent code won't make it any easier to make it
relocatable. It looks like the "bl 1f ; 1: mflr" sequence is used 13
times in arch/powerpc/kernel/*.S, I wonder if all of them are
unnecessary?
We support relocation of this kernel so any changes need to be tried
out w/CONFIG_RELOCATABLE enabled.
I'm fine with the patch as is and any other changes should be follow
on patches.
- k
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