[PATCH v4 3/3] LoongArch: Give chance to build under !CONFIG_SMP

[Tiezhu Yang]

In the current code, SMP is selected in Kconfig for LoongArch, the users
can not unset it, this is reasonable for a multiprocessor machine. But as
the help info of config SMP said, if you have a system with only one CPU,
say N. On a uniprocessor machine, the kernel will run faster if you say N
here.

The Loongson-2K0500 is a single-core CPU for applications like industrial
control, printing terminals, and BMC (Baseboard Management Controller),
there are many development boards, products and solutions on the market,
so it is better and necessary to give a chance to build under !CONFIG_SMP
for a uniprocessor machine.

First of all, do not select SMP for config LOONGARCH in Kconfig to make it
possible to unset CONFIG_SMP. Then, do some changes to fix the warnings and
errors if CONFIG_SMP is not set.

(1) Define get_ipi_irq() only if CONFIG_SMP is set to fix the warning:
arch/loongarch/kernel/irq.c:90:19: warning: 'get_ipi_irq' defined but not used [-Wunused-function]

(2) Add "#ifdef CONFIG_SMP" in asm/smp.h to fix the warning:
/arch/loongarch/include/asm/smp.h:49:9: warning: "raw_smp_processor_id" redefined
   49 | #define raw_smp_processor_id raw_smp_processor_id
      |         ^~~~~~~~~~~~~~~~~~~~
/include/linux/smp.h:198:9: note: this is the location of the previous definition
  198 | #define raw_smp_processor_id()                  0

(3) Define machine_shutdown() as empty under !CONFIG_SMP to fix the error:
arch/loongarch/kernel/machine_kexec.c: In function 'machine_shutdown':
arch/loongarch/kernel/machine_kexec.c:233:25: error: implicit declaration of function 'cpu_device_up'; did you mean 'put_device'? [-Wimplicit-function-declaration]

(4) Make config SCHED_SMT depends on SMP to fix many errors such as:
kernel/sched/core.c: In function 'sched_core_find':
kernel/sched/core.c:310:43: error: 'struct rq' has no member named 'cpu'

(5) Define cpu_logical_map(cpu) as read_csr_cpuid() under !CONFIG_SMP
in asm/smp.h and then include asm/smp.h in asm/acpi.h (because acpi.h
is included in linux/irq.h indirectly) to fix many build errors under
drivers/irqchip such as:
drivers/irqchip/irq-loongson-eiointc.c: In function 'cpu_to_eio_node':
drivers/irqchip/irq-loongson-eiointc.c:59:16: error: implicit declaration of function 'cpu_logical_map' [-Wimplicit-function-declaration]

When running the UnixBench tests with "-c 1" single-streamed pass,
the improvement in performance is about 9 percent with this patch.

By the way, it is helpful to debug and analysis the kernel issue
of multi-core system under !CONFIG_SMP.

Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
---
 arch/loongarch/Kconfig                | 2 +-
 arch/loongarch/include/asm/acpi.h     | 1 +
 arch/loongarch/include/asm/smp.h      | 5 +++++
 arch/loongarch/kernel/irq.c           | 2 ++
 arch/loongarch/kernel/machine_kexec.c | 2 +-
 5 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index a5f300ec6f28..8d892de0b7a8 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -174,7 +174,6 @@ config LOONGARCH
 	select PCI_QUIRKS
 	select PERF_USE_VMALLOC
 	select RTC_LIB
-	select SMP
 	select SPARSE_IRQ
 	select SYSCTL_ARCH_UNALIGN_ALLOW
 	select SYSCTL_ARCH_UNALIGN_NO_WARN
@@ -420,6 +419,7 @@ config EFI_STUB
 
 config SCHED_SMT
 	bool "SMT scheduler support"
+	depends on SMP
 	default y
 	help
 	  Improves scheduler's performance when there are multiple
diff --git a/arch/loongarch/include/asm/acpi.h b/arch/loongarch/include/asm/acpi.h
index 49e29b29996f..313f66f7913a 100644
--- a/arch/loongarch/include/asm/acpi.h
+++ b/arch/loongarch/include/asm/acpi.h
@@ -8,6 +8,7 @@
 #ifndef _ASM_LOONGARCH_ACPI_H
 #define _ASM_LOONGARCH_ACPI_H
 
+#include <asm/smp.h>
 #include <asm/suspend.h>
 
 #ifdef CONFIG_ACPI
diff --git a/arch/loongarch/include/asm/smp.h b/arch/loongarch/include/asm/smp.h
index f81e5f01d619..1ec11b57e60c 100644
--- a/arch/loongarch/include/asm/smp.h
+++ b/arch/loongarch/include/asm/smp.h
@@ -6,6 +6,7 @@
 #ifndef __ASM_SMP_H
 #define __ASM_SMP_H
 
+#ifdef CONFIG_SMP
 #include <linux/atomic.h>
 #include <linux/bitops.h>
 #include <linux/linkage.h>
@@ -101,4 +102,8 @@ static inline void __cpu_die(unsigned int cpu)
 }
 #endif
 
+#else /* !CONFIG_SMP */
+#define cpu_logical_map(cpu)	read_csr_cpuid()
+#endif /* CONFIG_SMP */
+
 #endif /* __ASM_SMP_H */
diff --git a/arch/loongarch/kernel/irq.c b/arch/loongarch/kernel/irq.c
index 883e5066ae44..e791fa275ec5 100644
--- a/arch/loongarch/kernel/irq.c
+++ b/arch/loongarch/kernel/irq.c
@@ -87,6 +87,7 @@ static void __init init_vec_parent_group(void)
 	acpi_table_parse(ACPI_SIG_MCFG, early_pci_mcfg_parse);
 }
 
+#ifdef CONFIG_SMP
 static int __init get_ipi_irq(void)
 {
 	struct irq_domain *d = irq_find_matching_fwnode(cpuintc_handle, DOMAIN_BUS_ANY);
@@ -96,6 +97,7 @@ static int __init get_ipi_irq(void)
 
 	return -EINVAL;
 }
+#endif
 
 void __init init_IRQ(void)
 {
diff --git a/arch/loongarch/kernel/machine_kexec.c b/arch/loongarch/kernel/machine_kexec.c
index 2dcb9e003657..8ae641dc53bb 100644
--- a/arch/loongarch/kernel/machine_kexec.c
+++ b/arch/loongarch/kernel/machine_kexec.c
@@ -225,6 +225,7 @@ void crash_smp_send_stop(void)
 
 void machine_shutdown(void)
 {
+#ifdef CONFIG_SMP
 	int cpu;
 
 	/* All CPUs go to reboot_code_buffer */
@@ -232,7 +233,6 @@ void machine_shutdown(void)
 		if (!cpu_online(cpu))
 			cpu_device_up(get_cpu_device(cpu));
 
-#ifdef CONFIG_SMP
 	smp_call_function(kexec_shutdown_secondary, NULL, 0);
 #endif
 }
-- 
2.42.0