irqchip fixes for 5.17, take #2

- Don't register a hotplug notifier on GICv3 systems that advertise
   LPI support, but have no ITS to make use of it
 
 - Add missing DT matching for the thead,c900-plic variant of the
   SiFive PLIC
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Merge tag 'irqchip-fixes-5.17-2' of git://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms into irq/urgent

Pull irqchip fixes from Marc Zyngier:

 - Don't register a hotplug notifier on GICv3 systems that advertise
   LPI support, but have no ITS to make use of it

 - Add missing DT matching for the thead,c900-plic variant of the
   SiFive PLIC

Link: https://lore.kernel.org/r/20220211110038.1179155-1-maz@kernel.org

Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.yaml

@@ -35,6 +35,10 @@ description:
   contains a specific memory layout, which is documented in chapter 8 of the
   SiFive U5 Coreplex Series Manual <https://static.dev.sifive.com/U54-MC-RVCoreIP.pdf>.
 
+  The thead,c900-plic is different from sifive,plic-1.0.0 in opensbi, the
+  T-HEAD PLIC implementation requires setting a delegation bit to allow access
+  from S-mode. So add thead,c900-plic to distinguish them.
+
 maintainers:
   - Sagar Kadam <sagar.kadam@sifive.com>
   - Paul Walmsley  <paul.walmsley@sifive.com>
@@ -42,12 +46,17 @@ maintainers:
 
 properties:
   compatible:
-    items:
-      - enum:
-          - sifive,fu540-c000-plic
-          - starfive,jh7100-plic
-          - canaan,k210-plic
-      - const: sifive,plic-1.0.0
+    oneOf:
+      - items:
+          - enum:
+              - sifive,fu540-c000-plic
+              - starfive,jh7100-plic
+              - canaan,k210-plic
+          - const: sifive,plic-1.0.0
+      - items:
+          - enum:
+              - allwinner,sun20i-d1-plic
+          - const: thead,c900-plic
 
   reg:
     maxItems: 1

drivers/irqchip/irq-gic-v3-its.c

@@ -5517,6 +5517,9 @@ int __init its_lpi_memreserve_init(void)
 	if (!efi_enabled(EFI_CONFIG_TABLES))
 		return 0;
 
+	if (list_empty(&its_nodes))
+		return 0;
+
 	gic_rdists->cpuhp_memreserve_state = CPUHP_INVALID;
 	state = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
 				  "irqchip/arm/gicv3/memreserve:online",

drivers/irqchip/irq-sifive-plic.c

@@ -398,3 +398,4 @@ out_free_priv:
 
 IRQCHIP_DECLARE(sifive_plic, "sifive,plic-1.0.0", plic_init);
 IRQCHIP_DECLARE(riscv_plic0, "riscv,plic0", plic_init); /* for legacy systems */
+IRQCHIP_DECLARE(thead_c900_plic, "thead,c900-plic", plic_init); /* for firmware driver */