linux-kernel - [PATCH] arm: allow single CPU configuration by adjusting NR

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Message-ID: <20250724172603.18701-1-suchitkarunakaran@gmail.com>
Date: Thu, 24 Jul 2025 22:56:03 +0530
From: Suchit Karunakaran <suchitkarunakaran@...il.com>
To: linux@...linux.org.uk,
	rmk+kernel@...linux.org.uk,
	ardb@...nel.org,
	linus.walleij@...aro.org,
	ebiggers@...gle.com,
	nathan@...nel.org,
	lumag@...nel.org,
	dave@...ilevsky.ca,
	ruanjinjie@...wei.com,
	kees@...nel.org,
	liuyuntao12@...wei.com,
	linux-arm-kernel@...ts.infradead.org
Cc: skhan@...uxfoundation.org,
	linux-kernel-mentees@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Suchit Karunakaran <suchitkarunakaran@...il.com>
Subject: [PATCH] arm: allow single CPU configuration by adjusting NR_CPUS range and defaults

Previously, the NR_CPUS config for ARM required a minimum of 2 CPUs.
This patch changes the minimum NR_CPUS to 1 when SMP is not enabled,
sets range to exactly 1 if !SMP, allowing only a single CPU setting and
adds conditional defaults:
    - default to 1 if SMP is disabled (uniprocessor)
    - default to 4 if SMP is enabled (multiprocessor)

Signed-off-by: Suchit Karunakaran <suchitkarunakaran@...il.com>
---
 arch/arm/Kconfig | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 3072731fe09c..23acee38721e 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1063,11 +1063,13 @@ config KASAN_SHADOW_OFFSET
 	default 0xffffffff
 
 config NR_CPUS
-	int "Maximum number of CPUs (2-32)"
+	int "Maximum number of CPUs (1-32)"
+	range 1 1 if !SMP
 	range 2 16 if DEBUG_KMAP_LOCAL
 	range 2 32 if !DEBUG_KMAP_LOCAL
 	depends on SMP
-	default "4"
+	default "1" if !SMP
+	default "4" if SMP
 	help
 	  The maximum number of CPUs that the kernel can support.
 	  Up to 32 CPUs can be supported, or up to 16 if kmap_local()
-- 
2.50.1