docs: arm64: gic-v5: Document booting requirements for GICv5

Document the requirements for booting a kernel on a system implementing
a GICv5 interrupt controller.

Specifically, other than DT/ACPI providing the required firmware
representation, define what traps must be disabled if the kernel is
booted at EL1 on a system where EL2 is implemented.

Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20250703-gicv5-host-v7-30-12e71f1b3528@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>

Author: Lorenzo Pieralisi

Documentation/arch/arm64/booting.rst

@@ -223,6 +223,47 @@ Before jumping into the kernel, the following conditions must be met:
 
     - SCR_EL3.HCE (bit 8) must be initialised to 0b1.
 
+  For systems with a GICv5 interrupt controller to be used in v5 mode:
+
+  - If the kernel is entered at EL1 and EL2 is present:
+
+      - ICH_HFGRTR_EL2.ICC_PPI_ACTIVERn_EL1 (bit 20) must be initialised to 0b1.
+      - ICH_HFGRTR_EL2.ICC_PPI_PRIORITYRn_EL1 (bit 19) must be initialised to 0b1.
+      - ICH_HFGRTR_EL2.ICC_PPI_PENDRn_EL1 (bit 18) must be initialised to 0b1.
+      - ICH_HFGRTR_EL2.ICC_PPI_ENABLERn_EL1 (bit 17) must be initialised to 0b1.
+      - ICH_HFGRTR_EL2.ICC_PPI_HMRn_EL1 (bit 16) must be initialised to 0b1.
+      - ICH_HFGRTR_EL2.ICC_IAFFIDR_EL1 (bit 7) must be initialised to 0b1.
+      - ICH_HFGRTR_EL2.ICC_ICSR_EL1 (bit 6) must be initialised to 0b1.
+      - ICH_HFGRTR_EL2.ICC_PCR_EL1 (bit 5) must be initialised to 0b1.
+      - ICH_HFGRTR_EL2.ICC_HPPIR_EL1 (bit 4) must be initialised to 0b1.
+      - ICH_HFGRTR_EL2.ICC_HAPR_EL1 (bit 3) must be initialised to 0b1.
+      - ICH_HFGRTR_EL2.ICC_CR0_EL1 (bit 2) must be initialised to 0b1.
+      - ICH_HFGRTR_EL2.ICC_IDRn_EL1 (bit 1) must be initialised to 0b1.
+      - ICH_HFGRTR_EL2.ICC_APR_EL1 (bit 0) must be initialised to 0b1.
+
+      - ICH_HFGWTR_EL2.ICC_PPI_ACTIVERn_EL1 (bit 20) must be initialised to 0b1.
+      - ICH_HFGWTR_EL2.ICC_PPI_PRIORITYRn_EL1 (bit 19) must be initialised to 0b1.
+      - ICH_HFGWTR_EL2.ICC_PPI_PENDRn_EL1 (bit 18) must be initialised to 0b1.
+      - ICH_HFGWTR_EL2.ICC_PPI_ENABLERn_EL1 (bit 17) must be initialised to 0b1.
+      - ICH_HFGWTR_EL2.ICC_ICSR_EL1 (bit 6) must be initialised to 0b1.
+      - ICH_HFGWTR_EL2.ICC_PCR_EL1 (bit 5) must be initialised to 0b1.
+      - ICH_HFGWTR_EL2.ICC_CR0_EL1 (bit 2) must be initialised to 0b1.
+      - ICH_HFGWTR_EL2.ICC_APR_EL1 (bit 0) must be initialised to 0b1.
+
+      - ICH_HFGITR_EL2.GICRCDNMIA (bit 10) must be initialised to 0b1.
+      - ICH_HFGITR_EL2.GICRCDIA (bit 9) must be initialised to 0b1.
+      - ICH_HFGITR_EL2.GICCDDI (bit 8) must be initialised to 0b1.
+      - ICH_HFGITR_EL2.GICCDEOI (bit 7) must be initialised to 0b1.
+      - ICH_HFGITR_EL2.GICCDHM (bit 6) must be initialised to 0b1.
+      - ICH_HFGITR_EL2.GICCDRCFG (bit 5) must be initialised to 0b1.
+      - ICH_HFGITR_EL2.GICCDPEND (bit 4) must be initialised to 0b1.
+      - ICH_HFGITR_EL2.GICCDAFF (bit 3) must be initialised to 0b1.
+      - ICH_HFGITR_EL2.GICCDPRI (bit 2) must be initialised to 0b1.
+      - ICH_HFGITR_EL2.GICCDDIS (bit 1) must be initialised to 0b1.
+      - ICH_HFGITR_EL2.GICCDEN (bit 0) must be initialised to 0b1.
+
+  - The DT or ACPI tables must describe a GICv5 interrupt controller.
+
   For systems with a GICv3 interrupt controller to be used in v3 mode:
   - If EL3 is present: