diff mbox series

[RFC,v3,05/21] ACPI: Rename ACPI_HOTPLUG_CPU to include 'present'

Message ID E1rDOgD-00Dvk2-3h@rmk-PC.armlinux.org.uk
State New
Headers
Series ACPI/arm64: add support for virtual cpu hotplug |

Commit Message

Russell King (Oracle) Dec. 13, 2023, 12:49 p.m. UTC 
  From: James Morse <james.morse@arm.com>

The code behind ACPI_HOTPLUG_CPU allows a not-present CPU to become
present. This isn't the only use of HOTPLUG_CPU. On arm64 and riscv
CPUs can be taken offline as a power saving measure.

On arm64 an offline CPU may be disabled by firmware, preventing it from
being brought back online, but it remains present throughout.

Adding code to prevent user-space trying to online these disabled CPUs
needs some additional terminology.

Rename the Kconfig symbol CONFIG_ACPI_HOTPLUG_PRESENT_CPU to reflect
that it makes possible CPUs present.

HOTPLUG_CPU is untouched as this is only about the ACPI mechanism.

Signed-off-by: James Morse <james.morse@arm.com>
Tested-by: Miguel Luis <miguel.luis@oracle.com>
Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
Tested-by: Jianyong Wu <jianyong.wu@arm.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
---
Changes since RFC v2:
 * Add Loongarch update
Changes since RFC v3:
 * Dropped ia64 changes
---
 arch/loongarch/Kconfig                     |  2 +-
 arch/loongarch/configs/loongson3_defconfig |  2 +-
 arch/loongarch/kernel/acpi.c               |  4 ++--
 arch/x86/Kconfig                           |  2 +-
 arch/x86/kernel/acpi/boot.c                |  4 ++--
 drivers/acpi/Kconfig                       |  4 ++--
 drivers/acpi/acpi_processor.c              | 10 +++++-----
 include/linux/acpi.h                       |  6 +++---
 8 files changed, 17 insertions(+), 17 deletions(-)

Comments

Jonathan Cameron Dec. 14, 2023, 5:41 p.m. UTC | #1 
On Wed, 13 Dec 2023 12:49:37 +0000
Russell King (Oracle) <rmk+kernel@armlinux.org.uk> wrote:

> From: James Morse <james.morse@arm.com>
> 
> The code behind ACPI_HOTPLUG_CPU allows a not-present CPU to become
> present. This isn't the only use of HOTPLUG_CPU. On arm64 and riscv
> CPUs can be taken offline as a power saving measure.
> 
> On arm64 an offline CPU may be disabled by firmware, preventing it from
> being brought back online, but it remains present throughout.
> 
> Adding code to prevent user-space trying to online these disabled CPUs
> needs some additional terminology.
> 
> Rename the Kconfig symbol CONFIG_ACPI_HOTPLUG_PRESENT_CPU to reflect
> that it makes possible CPUs present.
> 
> HOTPLUG_CPU is untouched as this is only about the ACPI mechanism.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> Tested-by: Miguel Luis <miguel.luis@oracle.com>
> Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> Tested-by: Jianyong Wu <jianyong.wu@arm.com>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Formatting nitpick inline. Either way FWIW:
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index 4db54e928b36..36071bc11acd 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h

>  #ifdef CONFIG_ACPI_HOTPLUG_IOAPIC
>  int acpi_get_ioapic_id(acpi_handle handle, u32 gsi_base, u64 *phys_addr);
> @@ -629,7 +629,7 @@ static inline u32 acpi_osc_ctx_get_cxl_control(struct acpi_osc_context *context)
>  #define ACPI_GSB_ACCESS_ATTRIB_RAW_PROCESS	0x0000000F
>  
>  /* Enable _OST when all relevant hotplug operations are enabled */
> -#if defined(CONFIG_ACPI_HOTPLUG_CPU) &&			\
> +#if defined(CONFIG_ACPI_HOTPLUG_PRESENT_CPU) &&			\

Trivial but I think there is a tab to many before that \

>  	defined(CONFIG_ACPI_HOTPLUG_MEMORY) &&		\
>  	defined(CONFIG_ACPI_CONTAINER)
>  #define ACPI_HOTPLUG_OST
Russell King (Oracle) Dec. 14, 2023, 6 p.m. UTC | #2 
On Thu, Dec 14, 2023 at 05:41:07PM +0000, Jonathan Cameron wrote:
> > Signed-off-by: James Morse <james.morse@arm.com>
> > Tested-by: Miguel Luis <miguel.luis@oracle.com>
> > Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> > Tested-by: Jianyong Wu <jianyong.wu@arm.com>
> > Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> Formatting nitpick inline. Either way FWIW:
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Thanks, but you're absolutely correct about the nitpick, so I've fixed
that too!
Rafael J. Wysocki Dec. 18, 2023, 8:35 p.m. UTC | #3 
On Wed, Dec 13, 2023 at 1:49 PM Russell King <rmk+kernel@armlinux.org.uk> wrote:
>
> From: James Morse <james.morse@arm.com>
>
> The code behind ACPI_HOTPLUG_CPU allows a not-present CPU to become
> present.

Right.

> This isn't the only use of HOTPLUG_CPU. On arm64 and riscv
> CPUs can be taken offline as a power saving measure.

But still there is the case in which a non-present CPU can become
present, isn't it there?

> On arm64 an offline CPU may be disabled by firmware, preventing it from
> being brought back online, but it remains present throughout.
>
> Adding code to prevent user-space trying to online these disabled CPUs
> needs some additional terminology.
>
> Rename the Kconfig symbol CONFIG_ACPI_HOTPLUG_PRESENT_CPU to reflect
> that it makes possible CPUs present.

Honestly, I don't think that this change is necessary or even useful.
Jonathan Cameron Jan. 22, 2024, 6 p.m. UTC | #4 
On Mon, 18 Dec 2023 21:35:16 +0100
"Rafael J. Wysocki" <rafael@kernel.org> wrote:

> On Wed, Dec 13, 2023 at 1:49 PM Russell King <rmk+kernel@armlinuxorg.uk> wrote:
> >
> > From: James Morse <james.morse@arm.com>
> >
> > The code behind ACPI_HOTPLUG_CPU allows a not-present CPU to become
> > present.  
> 
> Right.
> 
> > This isn't the only use of HOTPLUG_CPU. On arm64 and riscv
> > CPUs can be taken offline as a power saving measure.  
> 
> But still there is the case in which a non-present CPU can become
> present, isn't it there?

Not yet defined by the architectures (and I'm assuming it probably never will be).

The original proposal we took to ARM was to do exactly that - they pushed
back hard on the basis there was no architecturally safe way to implement it.
Too much of the ARM arch has to exist from the start of time.

https://lore.kernel.org/linux-arm-kernel/cbaa6d68-6143-e010-5f3c-ec62f879ad95@arm.com/
is one of the relevant threads of the kernel side of that discussion.

Not to put specific words into the ARM architects mouths, but the
short description is that there is currently no demand for working
out how to make physical CPU hotplug possible, as such they will not
provide an architecturally compliant way to do it for virtual CPU hotplug and
another means is needed (which is why this series doesn't use the present bit
for that purpose and we have the Online capable bit in MADT/GICC)

It was a 'fun' dance of several years to get to that clarification.
As another fun fact, the same is defined for x86, but I don't think
anyone has used it yet (GICC for ARM has an online capable bit in the flags to
enable this, which was remarkably similar to the online capable bit in the
flags of the Local APIC entries as added fairly recently).

> 
> > On arm64 an offline CPU may be disabled by firmware, preventing it from
> > being brought back online, but it remains present throughout.
> >
> > Adding code to prevent user-space trying to online these disabled CPUs
> > needs some additional terminology.
> >
> > Rename the Kconfig symbol CONFIG_ACPI_HOTPLUG_PRESENT_CPU to reflect
> > that it makes possible CPUs present.  
> 
> Honestly, I don't think that this change is necessary or even useful.

Whilst it's an attempt to avoid future confusion, the rename is
not something I really care about so my advice to Russell is drop
it unless you are attached to it!

Jonathan


> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
diff mbox series

Patch

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 15d05dd2b7f3..b1e87b90468d 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -5,7 +5,7 @@  config LOONGARCH
 	select ACPI
 	select ACPI_GENERIC_GSI if ACPI
 	select ACPI_MCFG if ACPI
-	select ACPI_HOTPLUG_CPU if ACPI_PROCESSOR && HOTPLUG_CPU
+	select ACPI_HOTPLUG_PRESENT_CPU if ACPI_PROCESSOR && HOTPLUG_CPU
 	select ACPI_PPTT if ACPI
 	select ACPI_SYSTEM_POWER_STATES_SUPPORT	if ACPI
 	select ARCH_BINFMT_ELF_STATE
diff --git a/arch/loongarch/configs/loongson3_defconfig b/arch/loongarch/configs/loongson3_defconfig
index 33795e4a5bd6..85d37b143077 100644
--- a/arch/loongarch/configs/loongson3_defconfig
+++ b/arch/loongarch/configs/loongson3_defconfig
@@ -59,7 +59,7 @@  CONFIG_ACPI_SPCR_TABLE=y
 CONFIG_ACPI_TAD=y
 CONFIG_ACPI_DOCK=y
 CONFIG_ACPI_IPMI=m
-CONFIG_ACPI_HOTPLUG_CPU=y
+CONFIG_ACPI_HOTPLUG_PRESENT_CPU=y
 CONFIG_ACPI_PCI_SLOT=y
 CONFIG_ACPI_HOTPLUG_MEMORY=y
 CONFIG_EFI_ZBOOT=y
diff --git a/arch/loongarch/kernel/acpi.c b/arch/loongarch/kernel/acpi.c
index 8e00a754e548..dfa56119b56f 100644
--- a/arch/loongarch/kernel/acpi.c
+++ b/arch/loongarch/kernel/acpi.c
@@ -288,7 +288,7 @@  void __init arch_reserve_mem_area(acpi_physical_address addr, size_t size)
 	memblock_reserve(addr, size);
 }
 
-#ifdef CONFIG_ACPI_HOTPLUG_CPU
+#ifdef CONFIG_ACPI_HOTPLUG_PRESENT_CPU
 
 #include <acpi/processor.h>
 
@@ -340,4 +340,4 @@  int acpi_unmap_cpu(int cpu)
 }
 EXPORT_SYMBOL(acpi_unmap_cpu);
 
-#endif /* CONFIG_ACPI_HOTPLUG_CPU */
+#endif /* CONFIG_ACPI_HOTPLUG_PRESENT_CPU */
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 8330c4ac26b3..64fc7c475ab0 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -59,7 +59,7 @@  config X86
 	#
 	select ACPI_LEGACY_TABLES_LOOKUP	if ACPI
 	select ACPI_SYSTEM_POWER_STATES_SUPPORT	if ACPI
-	select ACPI_HOTPLUG_CPU			if ACPI_PROCESSOR && HOTPLUG_CPU
+	select ACPI_HOTPLUG_PRESENT_CPU		if ACPI_PROCESSOR && HOTPLUG_CPU
 	select ARCH_32BIT_OFF_T			if X86_32
 	select ARCH_CLOCKSOURCE_INIT
 	select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index 1a0dd80d81ac..33d259ddd188 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -826,7 +826,7 @@  static void __init acpi_set_irq_model_ioapic(void)
 /*
  *  ACPI based hotplug support for CPU
  */
-#ifdef CONFIG_ACPI_HOTPLUG_CPU
+#ifdef CONFIG_ACPI_HOTPLUG_PRESENT_CPU
 #include <acpi/processor.h>
 
 static int acpi_map_cpu2node(acpi_handle handle, int cpu, int physid)
@@ -875,7 +875,7 @@  int acpi_unmap_cpu(int cpu)
 	return (0);
 }
 EXPORT_SYMBOL(acpi_unmap_cpu);
-#endif				/* CONFIG_ACPI_HOTPLUG_CPU */
+#endif				/* CONFIG_ACPI_HOTPLUG_PRESENT_CPU */
 
 int acpi_register_ioapic(acpi_handle handle, u64 phys_addr, u32 gsi_base)
 {
diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index a3acfc750fce..9c5a43d0aff4 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -306,7 +306,7 @@  config ACPI_IPMI
 	  To compile this driver as a module, choose M here:
 	  the module will be called as acpi_ipmi.
 
-config ACPI_HOTPLUG_CPU
+config ACPI_HOTPLUG_PRESENT_CPU
 	bool
 	depends on ACPI_PROCESSOR && HOTPLUG_CPU
 	select ACPI_CONTAINER
@@ -400,7 +400,7 @@  config ACPI_PCI_SLOT
 
 config ACPI_CONTAINER
 	bool "Container and Module Devices"
-	default (ACPI_HOTPLUG_MEMORY || ACPI_HOTPLUG_CPU)
+	default (ACPI_HOTPLUG_MEMORY || ACPI_HOTPLUG_PRESENT_CPU)
 	help
 	  This driver supports ACPI Container and Module devices (IDs
 	  ACPI0004, PNP0A05, and PNP0A06).
diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
index e7ed4730cbbe..c8e960ff0aca 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -183,7 +183,7 @@  static void __init acpi_pcc_cpufreq_init(void) {}
 #endif /* CONFIG_X86 */
 
 /* Initialization */
-#ifdef CONFIG_ACPI_HOTPLUG_CPU
+#ifdef CONFIG_ACPI_HOTPLUG_PRESENT_CPU
 static int acpi_processor_hotadd_init(struct acpi_processor *pr)
 {
 	unsigned long long sta;
@@ -228,7 +228,7 @@  static inline int acpi_processor_hotadd_init(struct acpi_processor *pr)
 {
 	return -ENODEV;
 }
-#endif /* CONFIG_ACPI_HOTPLUG_CPU */
+#endif /* CONFIG_ACPI_HOTPLUG_PRESENT_CPU */
 
 static int acpi_processor_get_info(struct acpi_device *device)
 {
@@ -461,7 +461,7 @@  static int acpi_processor_add(struct acpi_device *device,
 	return result;
 }
 
-#ifdef CONFIG_ACPI_HOTPLUG_CPU
+#ifdef CONFIG_ACPI_HOTPLUG_PRESENT_CPU
 /* Removal */
 static void acpi_processor_remove(struct acpi_device *device)
 {
@@ -505,7 +505,7 @@  static void acpi_processor_remove(struct acpi_device *device)
 	free_cpumask_var(pr->throttling.shared_cpu_map);
 	kfree(pr);
 }
-#endif /* CONFIG_ACPI_HOTPLUG_CPU */
+#endif /* CONFIG_ACPI_HOTPLUG_PRESENT_CPU */
 
 #ifdef CONFIG_ARCH_MIGHT_HAVE_ACPI_PDC
 bool __init processor_physically_present(acpi_handle handle)
@@ -630,7 +630,7 @@  static const struct acpi_device_id processor_device_ids[] = {
 static struct acpi_scan_handler processor_handler = {
 	.ids = processor_device_ids,
 	.attach = acpi_processor_add,
-#ifdef CONFIG_ACPI_HOTPLUG_CPU
+#ifdef CONFIG_ACPI_HOTPLUG_PRESENT_CPU
 	.detach = acpi_processor_remove,
 #endif
 	.hotplug = {
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 4db54e928b36..36071bc11acd 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -301,12 +301,12 @@  static inline int acpi_processor_evaluate_cst(acpi_handle handle, u32 cpu,
 }
 #endif
 
-#ifdef CONFIG_ACPI_HOTPLUG_CPU
+#ifdef CONFIG_ACPI_HOTPLUG_PRESENT_CPU
 /* Arch dependent functions for cpu hotplug support */
 int acpi_map_cpu(acpi_handle handle, phys_cpuid_t physid, u32 acpi_id,
 		 int *pcpu);
 int acpi_unmap_cpu(int cpu);
-#endif /* CONFIG_ACPI_HOTPLUG_CPU */
+#endif /* CONFIG_ACPI_HOTPLUG_PRESENT_CPU */
 
 #ifdef CONFIG_ACPI_HOTPLUG_IOAPIC
 int acpi_get_ioapic_id(acpi_handle handle, u32 gsi_base, u64 *phys_addr);
@@ -629,7 +629,7 @@  static inline u32 acpi_osc_ctx_get_cxl_control(struct acpi_osc_context *context)
 #define ACPI_GSB_ACCESS_ATTRIB_RAW_PROCESS	0x0000000F
 
 /* Enable _OST when all relevant hotplug operations are enabled */
-#if defined(CONFIG_ACPI_HOTPLUG_CPU) &&			\
+#if defined(CONFIG_ACPI_HOTPLUG_PRESENT_CPU) &&			\
 	defined(CONFIG_ACPI_HOTPLUG_MEMORY) &&		\
 	defined(CONFIG_ACPI_CONTAINER)
 #define ACPI_HOTPLUG_OST