linux-kernel - [PATCH v4 01/10] x86/acpi: Add a helper functions to setup and access the wakeup mailbox

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Message-Id: <20250603-rneri-wakeup-mailbox-v4-1-d533272b7232@linux.intel.com>
Date: Tue, 03 Jun 2025 17:15:13 -0700
From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To: x86@...nel.org, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, Rob Herring <robh@...nel.org>, 
 "K. Y. Srinivasan" <kys@...rosoft.com>, 
 Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>, 
 Dexuan Cui <decui@...rosoft.com>, Michael Kelley <mhklinux@...look.com>, 
 "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Saurabh Sengar <ssengar@...ux.microsoft.com>, 
 Chris Oo <cho@...rosoft.com>, 
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, 
 linux-hyperv@...r.kernel.org, devicetree@...r.kernel.org, 
 linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org, 
 "Ravi V. Shankar" <ravi.v.shankar@...el.com>, 
 Ricardo Neri <ricardo.neri@...el.com>, 
 Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Subject: [PATCH v4 01/10] x86/acpi: Add a helper functions to setup and
 access the wakeup mailbox

In preparation to move the functionality to wake secondary CPUs up out of
the ACPI code, add two helper functions.

The function acpi_setup_mp_wakeup_mailbox() stores the physical address of
the mailbox and updates the wakeup_secondary_cpu_64() APIC callback.

There is a slight change in behavior: now the APIC callback is updated
before configuring CPU hotplug offline behavior. This is fine as the APIC
callback continues to be updated unconditionally, regardless of the
restriction on CPU offlining.

The function acpi_madt_multiproc_wakeup_mailbox() returns a pointer to the
mailbox. Use this helper function only in the portions of the code for
which the variable acpi_mp_wake_mailbox will be out of scope once it is
relocated out of the ACPI directory.

The wakeup mailbox is only supported for CONFIG_X86_64 and needed only with
CONFIG_SMP=y.

Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
---
Changes since v3:
 - Squashed the two first patches of the series into one, both introduce
   helper functions. (Rafael)
 - Renamed setup_mp_wakeup_mailbox() as acpi_setup_mp_wakeup_mailbox().
   (Rafael)
 - Dropped the function prototype for !CONFIG_X86_64. (Rafael)

Changes since v2:
 - Introduced this patch.

Changes since v1:
 - N/A
---
 arch/x86/include/asm/smp.h         |  3 +++
 arch/x86/kernel/acpi/madt_wakeup.c | 20 +++++++++++++++-----
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index 0c1c68039d6f..77dce560a70a 100644
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -146,6 +146,9 @@ static inline struct cpumask *cpu_l2c_shared_mask(int cpu)
 	return per_cpu(cpu_l2c_shared_map, cpu);
 }

+void acpi_setup_mp_wakeup_mailbox(u64 addr);
+struct acpi_madt_multiproc_wakeup_mailbox *acpi_get_mp_wakeup_mailbox(void);
+
 #else /* !CONFIG_SMP */
 #define wbinvd_on_cpu(cpu)     wbinvd()
 static inline int wbinvd_on_all_cpus(void)
diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
index f36f28405dcc..4033c804307a 100644
--- a/arch/x86/kernel/acpi/madt_wakeup.c
+++ b/arch/x86/kernel/acpi/madt_wakeup.c
@@ -37,6 +37,7 @@ static void acpi_mp_play_dead(void)

 static void acpi_mp_cpu_die(unsigned int cpu)
 {
+	struct acpi_madt_multiproc_wakeup_mailbox *mailbox = acpi_get_mp_wakeup_mailbox();
 	u32 apicid = per_cpu(x86_cpu_to_apicid, cpu);
 	unsigned long timeout;

@@ -46,13 +47,13 @@ static void acpi_mp_cpu_die(unsigned int cpu)
 	 *
 	 * BIOS has to clear 'command' field of the mailbox.
 	 */
-	acpi_mp_wake_mailbox->apic_id = apicid;
-	smp_store_release(&acpi_mp_wake_mailbox->command,
+	mailbox->apic_id = apicid;
+	smp_store_release(&mailbox->command,
 			  ACPI_MP_WAKE_COMMAND_TEST);

 	/* Don't wait longer than a second. */
 	timeout = USEC_PER_SEC;
-	while (READ_ONCE(acpi_mp_wake_mailbox->command) && --timeout)
+	while (READ_ONCE(mailbox->command) && --timeout)
 		udelay(1);

 	if (!timeout)
@@ -227,7 +228,7 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,

 	acpi_table_print_madt_entry(&header->common);

-	acpi_mp_wake_mailbox_paddr = mp_wake->mailbox_address;
+	acpi_setup_mp_wakeup_mailbox(mp_wake->mailbox_address);

 	if (mp_wake->version >= ACPI_MADT_MP_WAKEUP_VERSION_V1 &&
 	    mp_wake->header.length >= ACPI_MADT_MP_WAKEUP_SIZE_V1) {
@@ -243,7 +244,16 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
 		acpi_mp_disable_offlining(mp_wake);
 	}

+	return 0;
+}
+
+void __init acpi_setup_mp_wakeup_mailbox(u64 mailbox_paddr)
+{
+	acpi_mp_wake_mailbox_paddr = mailbox_paddr;
 	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
+}

-	return 0;
+struct acpi_madt_multiproc_wakeup_mailbox *acpi_get_mp_wakeup_mailbox(void)
+{
+	return acpi_mp_wake_mailbox;
 }

-- 
2.43.0