[PATCH 03/11] x86: Kconfig.cpu: split out 64-bit atom

[Arnd Bergmann <arnd@kernel.org>]

From: Arnd Bergmann <arnd@arndb.de>

Both 32-bit and 64-bit builds allow optimizing using "-march=atom", but
this is somewhat suboptimal, as gcc and clang use this option to refer
to the original in-order "Bonnell" microarchitecture used in the early
"Diamondville" and "Silverthorne" processors that were mostly 32-bit only.

The later 22nm "Silvermont" architecture saw a significant redesign to
an out-of-order architecture that is reflected in the -mtune=silvermont
flag in the compilers, and all of these are 64-bit capable. Variations
of this microarchitecture were in CPUs launched from 2014 to 2021 and
are still common in 2024.

Split this up so that 32-bit targets keep building with -march=atom,
but 64-bit ones get the more useful silvermont optimization. On modern
"tremont" and newer CPUs, using -march=generic or -march=tremont
would be even better, but the silvermont optimization is still an
improvement.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 arch/x86/Kconfig.cpu     | 28 ++++++++++++++++++++--------
 arch/x86/Makefile        |  4 ++--
 arch/x86/Makefile_32.cpu |  3 +--
 3 files changed, 23 insertions(+), 12 deletions(-)

diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu
index 42e6a40876ea..05a3f57ac20b 100644
--- a/arch/x86/Kconfig.cpu
+++ b/arch/x86/Kconfig.cpu
@@ -155,6 +155,15 @@ config MPENTIUM4
 		-Paxville
 		-Dempsey
 
+config MATOM
+	bool "Intel Atom (Bonnell)"
+	help
+
+	  Select this for the Intel Atom platform. Intel Atom CPUs have an
+	  in-order pipelining architecture and thus can benefit from
+	  accordingly optimized code.
+	  This includes all the 32-bit-only Atom chips such as N2xx and
+	  Z5xx/Z6xx.
 
 config MK6
 	bool "K6/K6-II/K6-III"
@@ -278,14 +287,17 @@ config MCORE2
 	  family in /proc/cpuinfo. Newer ones have 6 and older ones 15
 	  (not a typo)
 
-config MATOM
-	bool "Intel Atom"
+config MSILVERMONT
+	bool "Intel Atom (Silvermont/Goldmont)"
+	depends on X86_64
 	help
-
-	  Select this for the Intel Atom platform. Intel Atom CPUs have an
-	  in-order pipelining architecture and thus can benefit from
-	  accordingly optimized code. Use a recent GCC with specific Atom
-	  support in order to fully benefit from selecting this option.
+	  Select this to optimize for the 64-bit Intel Atom platform
+	  of the 22nm Silvermont microarchitecture and its 14nm
+	  Goldmont shrink (e.g. Atom C2xxx, Atom Z3xxx, Celeron
+	  N2xxx/J1xxx, Pentium N3xxx/J2xxx).
+	  Kernels built with this option are incompatible with very
+	  early Atom CPUs based on the Bonnell microarchitecture,
+	  such as Atom 230/330, D4xx/D5xx, D2xxx, N2xxx or Z2xxx.
 
 config GENERIC_CPU
 	bool "Generic-x86-64"
@@ -318,7 +330,7 @@ config X86_INTERNODE_CACHE_SHIFT
 config X86_L1_CACHE_SHIFT
 	int
 	default "7" if MPENTIUM4 || MPSC
-	default "6" if MK7 || MK8 || MPENTIUMM || MCORE2 || MATOM || MVIAC7 || X86_GENERIC || GENERIC_CPU
+	default "6" if MK7 || MK8 || MPENTIUMM || MCORE2 || MATOM || MSILVERMONT || MVIAC7 || X86_GENERIC || GENERIC_CPU
 	default "4" if MELAN || M486SX || M486 || MGEODEGX1
 	default "5" if MWINCHIP3D || MWINCHIPC6 || MCRUSOE || MEFFICEON || MCYRIXIII || MK6 || MPENTIUMIII || MPENTIUMII || M686 || M586MMX || M586TSC || M586 || MVIAC3_2 || MGEODE_LX
 
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 5b773b34768d..05887ae282f5 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -182,14 +182,14 @@ else
         cflags-$(CONFIG_MK8)		+= -march=k8
         cflags-$(CONFIG_MPSC)		+= -march=nocona
         cflags-$(CONFIG_MCORE2)		+= -march=core2
-        cflags-$(CONFIG_MATOM)		+= -march=atom
+        cflags-$(CONFIG_MSILVERMONT)	+= -march=silvermont
         cflags-$(CONFIG_GENERIC_CPU)	+= -mtune=generic
         KBUILD_CFLAGS += $(cflags-y)
 
         rustflags-$(CONFIG_MK8)		+= -Ctarget-cpu=k8
         rustflags-$(CONFIG_MPSC)	+= -Ctarget-cpu=nocona
         rustflags-$(CONFIG_MCORE2)	+= -Ctarget-cpu=core2
-        rustflags-$(CONFIG_MATOM)	+= -Ctarget-cpu=atom
+        rustflags-$(CONFIG_MSILVERMONT)	+= -Ctarget-cpu=silvermont
         rustflags-$(CONFIG_GENERIC_CPU)	+= -Ztune-cpu=generic
         KBUILD_RUSTFLAGS += $(rustflags-y)
 
diff --git a/arch/x86/Makefile_32.cpu b/arch/x86/Makefile_32.cpu
index 94834c4b5e5e..0adc3a59520a 100644
--- a/arch/x86/Makefile_32.cpu
+++ b/arch/x86/Makefile_32.cpu
@@ -33,8 +33,7 @@ cflags-$(CONFIG_MCYRIXIII)	+= $(call cc-option,-march=c3,-march=i486) $(align)
 cflags-$(CONFIG_MVIAC3_2)	+= $(call cc-option,-march=c3-2,-march=i686)
 cflags-$(CONFIG_MVIAC7)		+= -march=i686
 cflags-$(CONFIG_MCORE2)		+= -march=i686 $(call tune,core2)
-cflags-$(CONFIG_MATOM)		+= $(call cc-option,-march=atom,$(call cc-option,-march=core2,-march=i686)) \
-	$(call cc-option,-mtune=atom,$(call cc-option,-mtune=generic))
+cflags-$(CONFIG_MATOM)		+= -march=atom
 
 # AMD Elan support
 cflags-$(CONFIG_MELAN)		+= -march=i486
-- 
2.39.5