Hi Grant,
My point is that IDTLBT (see page 7-65 in the PA-RISC 2.0w spec) expects
the U-bit in 12th bit of the 64-bit DWORD, thus, in the upper part
instead of the lower part (see the code at dtlb_miss_20w). As you said,
the bit is set in the lower part. I still suspect that the wrong bit is
set on a 64-bit machine.
The confusion comes from the fact that the The PA1.1 instruction IDTLBP
expects U-bit in the bit 12 of the WORD, whereas PA2.0 IDTLBT expects
it in bit 12 of the DWORD.
Best regards,
Artem
Grant Grundler wrote:
On Thu, Jul 09, 2009 at 03:11:19PM +0200, Artem Alimarine wrote:
Hi guys,
I am new to PARISC and to this forum. I have a small question. There is
an instruction in entry.S that I do not understand. It is in the the
macro make_insert_tlb
Kernel 2.6.26.2:
537 /* Enforce uncacheable pages.
538 * This should ONLY be use for MMIO on PA 2.0 machines.
539 * Memory/DMA is cache coherent on all PA2.0 machines we support
540 * (that means T-class is NOT supported) and the memory controllers
541 * on most of those machines only handles cache transactions.
542 */
543 extrd,u,*= \pte,_PAGE_NO_CACHE_BIT+32,1,%r0
544 depi 1,12,1,\prot
The "*=" in line 543 will determine if "depi" instruction (line 544)
gets executed or not. You'll need the "PA-RISC 2.0 Architecture":
http://www.parisc-linux.org/documentation/index.html
http://ftp.parisc-linux.org/docs/arch/parisc2.0.pdf
And read page 7-47, 7-48, and Table D-14.
The DEPI instruction on a 64-bit machine sets bit 44=32+12,
whereas we use the value as the argument to IDTLBT, which expects bit 12
to be used instead.
Does it mean that the U-bit is never set and the
authorization id gets corrupted???
U-bit will get set only if _PAGE_NO_CACHE_BIT+32 is also set.
The bit enumeration is *reverse* with MSb being 0 for all ASM instructions
and all references in the PA2.0 Arch manual.
Because this is a 64 bit build, "+32" is needed to refer to the lower half
of the double word (word == 32 bits).
Is it a bug or my misunderstanding of the code???
It looks correct to me. "12" here always seems to refer to the U-bit as
defined in the PA2.0 Arch manual.
hth,
grant
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