PCI: dwc: Enable MSI affinity support

Leverage the interrupt redirection infrastructure to enable CPU affinity
support for MSI interrupts. Since the parent interrupt affinity cannot
be changed, affinity control for the child interrupt (MSI) is achieved
by redirecting the handler to run in IRQ work context on the target CPU.

This patch was originally prepared by Thomas Gleixner (see Link tag below)
in a patch series that was never submitted as is, and only parts of that
series have made it upstream so far.

Originally-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Radu Rendec <rrendec@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/linux-pci/878qpg4o4t.ffs@tglx/
Link: https://patch.msgid.link/20251128212055.1409093-4-rrendec@redhat.com

Author: rrendec

drivers/pci/controller/dwc/pcie-designware-host.c

@@ -26,9 +26,27 @@ static struct pci_ops dw_pcie_ops;
 static struct pci_ops dw_pcie_ecam_ops;
 static struct pci_ops dw_child_pcie_ops;
 
+#ifdef CONFIG_SMP
+static void dw_irq_noop(struct irq_data *d) { }
+#endif
+
+static bool dw_pcie_init_dev_msi_info(struct device *dev, struct irq_domain *domain,
+				      struct irq_domain *real_parent, struct msi_domain_info *info)
+{
+	if (!msi_lib_init_dev_msi_info(dev, domain, real_parent, info))
+		return false;
+
+#ifdef CONFIG_SMP
+	info->chip->irq_ack = dw_irq_noop;
+	info->chip->irq_pre_redirect = irq_chip_pre_redirect_parent;
+#else
+	info->chip->irq_ack = irq_chip_ack_parent;
+#endif
+	return true;
+}
+
 #define DW_PCIE_MSI_FLAGS_REQUIRED (MSI_FLAG_USE_DEF_DOM_OPS		| \
 				    MSI_FLAG_USE_DEF_CHIP_OPS		| \
-				    MSI_FLAG_NO_AFFINITY		| \
 				    MSI_FLAG_PCI_MSI_MASK_PARENT)
 #define DW_PCIE_MSI_FLAGS_SUPPORTED (MSI_FLAG_MULTI_PCI_MSI		| \
 				     MSI_FLAG_PCI_MSIX			| \
@@ -40,9 +58,8 @@ static const struct msi_parent_ops dw_pcie_msi_parent_ops = {
 	.required_flags		= DW_PCIE_MSI_FLAGS_REQUIRED,
 	.supported_flags	= DW_PCIE_MSI_FLAGS_SUPPORTED,
 	.bus_select_token	= DOMAIN_BUS_PCI_MSI,
-	.chip_flags		= MSI_CHIP_FLAG_SET_ACK,
 	.prefix			= "DW-",
-	.init_dev_msi_info	= msi_lib_init_dev_msi_info,
+	.init_dev_msi_info	= dw_pcie_init_dev_msi_info,
 };
 
 /* MSI int handler */
@@ -63,7 +80,7 @@ void dw_handle_msi_irq(struct dw_pcie_rp *pp)
 			continue;
 
 		for_each_set_bit(pos, &status, MAX_MSI_IRQS_PER_CTRL)
-			generic_handle_domain_irq(pp->irq_domain, irq_off + pos);
+			generic_handle_demux_domain_irq(pp->irq_domain, irq_off + pos);
 	}
 }
 
@@ -140,10 +157,16 @@ static void dw_pci_bottom_ack(struct irq_data *d)
 
 static struct irq_chip dw_pci_msi_bottom_irq_chip = {
 	.name			= "DWPCI-MSI",
-	.irq_ack		= dw_pci_bottom_ack,
 	.irq_compose_msi_msg	= dw_pci_setup_msi_msg,
 	.irq_mask		= dw_pci_bottom_mask,
 	.irq_unmask		= dw_pci_bottom_unmask,
+#ifdef CONFIG_SMP
+	.irq_ack		= dw_irq_noop,
+	.irq_pre_redirect	= dw_pci_bottom_ack,
+	.irq_set_affinity	= irq_chip_redirect_set_affinity,
+#else
+	.irq_ack		= dw_pci_bottom_ack,
+#endif
 };
 
 static int dw_pcie_irq_domain_alloc(struct irq_domain *domain, unsigned int virq,