Re: sys/powerpc64: encode PTCR PATS correctly

On Wed, 08 Jul 2026 00:35:32 +0200,
Kirill A. Korinsky <[email protected]> wrote:
> 
> Mark, George,
> 
> Shivang Upadhyay in qemu-devel
> https://marc.info/?l=qemu-devel&m=178332702820587&w=2 pointed that we may
> have a typo kind of bug in powerpc64's pmap.
> 
> The PTCR PATS field stores log2(partition table size) - 12.  Since
> PATMEMSZ is a power of two, ffs(PATMEMSZ) is log2(PATMEMSZ) + 1; the
> old expression wrote 5 for the 64 KiB table, describing 128 KiB to
> Book3S v3 hardware.
> 
> Use fls(PATMEMSZ) - 1 - 12 to express the intended log2 calculation
> and encode the 64 KiB partition table as PATS == 4.
> 
> Ok?
> 

Ping?

Index: sys/arch/powerpc64/powerpc64/pmap.c
===================================================================
RCS file: /home/cvs/src/sys/arch/powerpc64/powerpc64/pmap.c,v
diff -u -p -r1.66 pmap.c
--- sys/arch/powerpc64/powerpc64/pmap.c	21 Aug 2025 00:10:21 -0000	1.66
+++ sys/arch/powerpc64/powerpc64/pmap.c	7 Jul 2026 20:20:55 -0000
@@ -124,7 +124,7 @@ uint64_t pmap_ptab_mask;
 struct pate *pmap_pat;
 
 #define PATMEMSZ	(64 * 1024)
-#define PATSIZE		(ffs(PATMEMSZ) - 12)
+#define PATSIZE		(fls(PATMEMSZ) - 1 - 12)
 
 struct pte_desc {
 	/* Linked list of phys -> virt entries */


-- 
wbr, Kirill