linux-kernel - [PATCH v3] RISC-V: Increase range and default value of NR

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Date:   Wed, 20 Apr 2022 16:54:08 +0530
From:   Anup Patel <apatel@...tanamicro.com>
To:     Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Atish Patra <atishp@...shpatra.org>,
        Alistair Francis <Alistair.Francis@....com>,
        Heinrich Schuchardt <heinrich.schuchardt@...onical.com>,
        Anup Patel <anup@...infault.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Anup Patel <apatel@...tanamicro.com>
Subject: [PATCH v3] RISC-V: Increase range and default value of NR_CPUS

Currently, the range and default value of NR_CPUS is too restrictive
for high-end RISC-V systems with large number of HARTs. The latest
QEMU virt machine supports upto 512 CPUs so the current NR_CPUS is
restrictive for QEMU as well. Other major architectures (such as
ARM64, x86_64, MIPS, etc) have a much higher range and default
value of NR_CPUS.

This patch increases NR_CPUS range to 2-512 and default value to
XLEN (i.e. 32 for RV32 and 64 for RV64).

Signed-off-by: Anup Patel <apatel@...tanamicro.com>
---
Changes since v2:
 - Rebased on Linux-5.18-rc3
 - Use a different range when SBI v0.1 is enabled
Changes since v1:
 - Updated NR_CPUS range to 2-512 which reflects maximum number of
   CPUs supported by QEMU virt machine.
---
 arch/riscv/Kconfig | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 00fd9c548f26..1823f281069f 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -275,10 +275,13 @@ config SMP
 	  If you don't know what to do here, say N.
 
 config NR_CPUS
-	int "Maximum number of CPUs (2-32)"
-	range 2 32
+	int "Maximum number of CPUs (2-512)"
 	depends on SMP
-	default "8"
+	range 2 512 if !SBI_V01
+	range 2 32 if SBI_V01 && 32BIT
+	range 2 64 if SBI_V01 && 64BIT
+	default "32" if 32BIT
+	default "64" if 64BIT
 
 config HOTPLUG_CPU
 	bool "Support for hot-pluggable CPUs"
-- 
2.25.1