On 27.02.23 20:46, Geert Uytterhoeven wrote:

Hi David,

On Mon, Feb 27, 2023 at 6:01 PM David Hildenbrand [off-list ref] wrote:

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    /*
     * Externally used page protection values.

diff --git a/arch/microblaze/include/asm/pgtable.h b/arch/microblaze/include/asm/pgtable.h
index 42f5988e998b..7e3de54bf426 100644
--- a/arch/microblaze/include/asm/pgtable.h
+++ b/arch/microblaze/include/asm/pgtable.h

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     * - All other bits of the PTE are loaded into TLBLO without
     *  * modification, leaving us only the bits 20, 21, 24, 25, 26, 30 for
     * software PTE bits.  We actually use bits 21, 24, 25, and

@@ -155,6 +155,9 @@ extern pte_t *va_to_pte(unsigned long address);
    #define _PAGE_ACCESSED 0x400   /* software: R: page referenced */
    #define _PMD_PRESENT   PAGE_MASK

+/* We borrow bit 24 to store the exclusive marker in swap PTEs. */
+#define _PAGE_SWP_EXCLUSIVE    _PAGE_DIRTY

_PAGE_DIRTY is 0x80, so this is also bit 7, thus the new comment is
wrong?

In the example, I use MSB-0 bit numbering (which I determined to be
correct in microblaze context eventually, but I got confused a couple a
times because it's very inconsistent). That should be MSB-0 bit 24.

Thanks, TIL microblaze uses IBM bit numbering...

I assume IBM bit numbering corresponds to MSB-0 bit numbering, correct?

Correct, as seen in s370 and PowerPC manuals...

Good, I have some solid s390x background, but thinking about the term 
"IBM PC" made me double-check that we're talking about the same thing ;)

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I recall that I used the comment above "/* Definitions for MicroBlaze.
*/" as an orientation.

0  1  2  3  4  ... 18 19 20 21 22 23 24 25 26 27 28 29 30 31
RPN.....................  0  0 EX WR ZSEL.......  W  I  M  G

Indeed, that's where I noticed the "unconventional" numbering...

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So ... either we adjust both or we leave it as is. (again, depends on
what the right thing to to is -- which I don't know :) )

It depends whether you want to match the hardware documentation,
or the Linux BIT() macro and friends...

The hardware documentation, so we should be good.

Thanks!

-- 
Thanks,

David / dhildenb


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