linux-kernel - [PATCH v7 31/37] armv8: cpu: Enable ACPI parking protocol

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Message-ID: <20241011102419.12523-32-patrick.rudolph@9elements.com>
Date: Fri, 11 Oct 2024 12:23:12 +0200
From: Patrick Rudolph <patrick.rudolph@...ements.com>
To: u-boot@...ts.denx.de,
	linux-kernel@...r.kernel.org
Cc: Patrick Rudolph <patrick.rudolph@...ements.com>,
	Simon Glass <sjg@...omium.org>,
	Tom Rini <trini@...sulko.com>
Subject: [PATCH v7 31/37] armv8: cpu: Enable ACPI parking protocol

Update the generic entry point code to support the ACPI parking protocol.
The ACPI parking protocol can be used when PSCI is not available to bring
up secondary CPU cores.

When enabled secondary CPUs will enter U-Boot proper and spin in their own
4KiB reserved memory page, which also acts as mailbox with the OS to
release the CPU.

TEST: Boots all CPUs on qemu-system-aarch64 -machine raspi4b

Signed-off-by: Patrick Rudolph <patrick.rudolph@...ements.com>
Reviewed-by: Simon Glass <sjg@...omium.org>
---
 arch/arm/cpu/armv8/start.S | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/arm/cpu/armv8/start.S b/arch/arm/cpu/armv8/start.S
index 7461280261..544a4a5364 100644
--- a/arch/arm/cpu/armv8/start.S
+++ b/arch/arm/cpu/armv8/start.S
@@ -178,6 +178,18 @@ pie_fixup_done:
 	branch_if_master x0, master_cpu
 	b	spin_table_secondary_jump
 	/* never return */
+#elif defined(CONFIG_ACPI_PARKING_PROTOCOL) && !defined(CONFIG_SPL_BUILD)
+	branch_if_master x0, master_cpu
+	/*
+	 * Waits for ACPI parking protocol memory to be allocated and the spin-table
+	 * code to be written. Once ready the secondary CPUs will jump and spin in
+	 * their own 4KiB memory region, which is also used as mailbox, until released
+	 * by the OS.
+	 * The mechanism is similar to the DT enable-method = "spin-table", but works
+	 * with ACPI enabled platforms.
+	 */
+	b	acpi_pp_secondary_jump
+	/* never return */
 #elif defined(CONFIG_ARMV8_MULTIENTRY)
 	branch_if_master x0, master_cpu
 
-- 
2.46.2