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x86/cpu: Drop vestigial PBE logic in AMD/Hygon/Centaur/Cyrix

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Besides formatting changes, this logic dates back to Linux 2.4.0-test11 in
November 2000.

Prior to "Massive cleanup of CPU detection and bug handling",
c->x86_capability was a single u32 containing cpuid(1).edx,
cpuid(0x80000001).edx, or a synthesis thereof.  X86_FEATURE_AMD3D was
defined as the top bit this single u32.

After "Massive cleanup of CPU detection and bug handling",
c->x86_capability became an array with AMD's extended feature leaf split
away from Intel's basic feature leaf.

AMD doc #20734-G states that 3DNow is only enumerated in the extended
feature leaf, and that other vendors where using this bit too.  i.e. AMD
never produced a CPU which set bit 31 in the basic leaf, meaning that
there's nothing to clear out in the first place.

This logic looks like it was relevant in the pre-"Massive cleanup" world
but ought to have been dropped when c->x86_capability was properly split.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Pu Wen <puwen@hygon.cn>
Link: https://patch.msgid.link/20251126125147.880275-1-andrew.cooper3@citrix.com
This commit is contained in:
Andrew Cooper 2025-11-26 12:51:47 +00:00 committed by Ingo Molnar
parent a2aabcfc60
commit 0bc03750de
4 changed files with 0 additions and 24 deletions
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6
arch/x86/kernel/cpu/amd.c
View File

@ -1051,12 +1051,6 @@ static void init_amd(struct cpuinfo_x86 *c)
early_init_amd(c);
/*
* Bit 31 in normal CPUID used for nonstandard 3DNow ID;
* 3DNow is IDd by bit 31 in extended CPUID (1*32+31) anyway
*/
clear_cpu_cap(c, 0*32+31);
if (c->x86 >= 0x10)
set_cpu_cap(c, X86_FEATURE_REP_GOOD);

6
arch/x86/kernel/cpu/centaur.c
View File

@ -119,12 +119,6 @@ static void init_centaur(struct cpuinfo_x86 *c)
u32 fcr_clr = 0;
u32 lo, hi, newlo;
u32 aa, bb, cc, dd;
/*
* Bit 31 in normal CPUID used for nonstandard 3DNow ID;
* 3DNow is IDd by bit 31 in extended CPUID (1*32+31) anyway
*/
clear_cpu_cap(c, 0*32+31);
#endif
early_init_centaur(c);
init_intel_cacheinfo(c);

6
arch/x86/kernel/cpu/cyrix.c
View File

@ -195,12 +195,6 @@ static void init_cyrix(struct cpuinfo_x86 *c)
char *buf = c->x86_model_id;
const char *p = NULL;
/*
* Bit 31 in normal CPUID used for nonstandard 3DNow ID;
* 3DNow is IDd by bit 31 in extended CPUID (1*32+31) anyway
*/
clear_cpu_cap(c, 0*32+31);
/* Cyrix used bit 24 in extended (AMD) CPUID for Cyrix MMX extensions */
if (test_cpu_cap(c, 1*32+24)) {
clear_cpu_cap(c, 1*32+24);

6
arch/x86/kernel/cpu/hygon.c
View File

@ -174,12 +174,6 @@ static void init_hygon(struct cpuinfo_x86 *c)
early_init_hygon(c);
/*
* Bit 31 in normal CPUID used for nonstandard 3DNow ID;
* 3DNow is IDd by bit 31 in extended CPUID (1*32+31) anyway
*/
clear_cpu_cap(c, 0*32+31);
set_cpu_cap(c, X86_FEATURE_REP_GOOD);
/*