irqchip/riscv-aplic: Prevent crash when MSI domain is missing

If the APLIC driver is probed before the IMSIC driver, the parent MSI
domain will be missing, which causes a NULL pointer dereference in
msi_create_device_irq_domain().

Avoid this by deferring probe until the parent MSI domain is available. Use
dev_err_probe() to avoid printing an error message when returning
-EPROBE_DEFER.

Fixes: ca8df97fe6 ("irqchip/riscv-aplic: Add support for MSI-mode")
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20241114200133.3069460-1-samuel.holland@sifive.com

drivers/irqchip/irq-riscv-aplic-main.c

@@ -207,7 +207,8 @@ static int aplic_probe(struct platform_device *pdev)
 	else
 		rc = aplic_direct_setup(dev, regs);
 	if (rc)
-		dev_err(dev, "failed to setup APLIC in %s mode\n", msi_mode ? "MSI" : "direct");
+		dev_err_probe(dev, rc, "failed to setup APLIC in %s mode\n",
+			      msi_mode ? "MSI" : "direct");
 
 #ifdef CONFIG_ACPI
 	if (!acpi_disabled)

drivers/irqchip/irq-riscv-aplic-msi.c

@@ -266,6 +266,9 @@ int aplic_msi_setup(struct device *dev, void __iomem *regs)
 			if (msi_domain)
 				dev_set_msi_domain(dev, msi_domain);
 		}
+
+		if (!dev_get_msi_domain(dev))
+			return -EPROBE_DEFER;
 	}
 
 	if (!msi_create_device_irq_domain(dev, MSI_DEFAULT_DOMAIN, &aplic_msi_template,