irqchip/gic-v3: Add PCI/MSI support to the GICv3 MBI sub-driver

You would hope that if you have a GICv3 in your system, you'd use the ITS,
as it provides a large interrupt ID space and device isolation. Sadly,
some SoC integrations are less than perfect, and the ITS is not usesable on
those.

The only solution for these systems is to use the MBI interface, and
rely on a very small number of possible vectors.

This patch thus adds minimal support for PCI/MSI on top of the GICv3
MBI driver. Please don't use it if you can avoid it.

Signed-off-by: Marc Zyngier <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Tested-by: Ard Biesheuvel <[e-mail]>
Tested-by: Srinivas Kandagatla <[e-mail]>
Cc: Rob Herring <[e-mail]>
Cc: Jason Cooper <[e-mail]>
Cc: Thomas Petazzoni <[e-mail]>
Cc: Miquel Raynal <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

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

···
 #include <linux/kernel.h>
 #include <linux/msi.h>
 #include <linux/of_address.h>
+#include <linux/of_pci.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 
···
 	iommu_dma_map_msi_msg(data->irq, msg);
 }
 
+#ifdef CONFIG_PCI_MSI
+/* PCI-specific irqchip */
+static void mbi_mask_msi_irq(struct irq_data *d)
+{
+	pci_msi_mask_irq(d);
+	irq_chip_mask_parent(d);
+}
+
+static void mbi_unmask_msi_irq(struct irq_data *d)
+{
+	pci_msi_unmask_irq(d);
+	irq_chip_unmask_parent(d);
+}
+
+static struct irq_chip mbi_msi_irq_chip = {
+	.name			= "MSI",
+	.irq_mask		= mbi_mask_msi_irq,
+	.irq_unmask		= mbi_unmask_msi_irq,
+	.irq_eoi		= irq_chip_eoi_parent,
+	.irq_compose_msi_msg	= mbi_compose_msi_msg,
+	.irq_write_msi_msg	= pci_msi_domain_write_msg,
+};
+
+static struct msi_domain_info mbi_msi_domain_info = {
+	.flags	= (MSI_FLAG_USE_DEF_DOM_OPS | MSI_FLAG_USE_DEF_CHIP_OPS |
+		   MSI_FLAG_PCI_MSIX | MSI_FLAG_MULTI_PCI_MSI),
+	.chip	= &mbi_msi_irq_chip,
+};
+
+static int mbi_allocate_pci_domain(struct irq_domain *nexus_domain,
+				   struct irq_domain **pci_domain)
+{
+	*pci_domain = pci_msi_create_irq_domain(nexus_domain->parent->fwnode,
+						&mbi_msi_domain_info,
+						nexus_domain);
+	if (!*pci_domain)
+		return -ENOMEM;
+
+	return 0;
+}
+#else
+static int mbi_allocate_pci_domain(struct irq_domain *nexus_domain,
+				   struct irq_domain **pci_domain)
+{
+	*pci_domain = NULL;
+	return 0;
+}
+#endif
+
 static void mbi_compose_mbi_msg(struct irq_data *data, struct msi_msg *msg)
 {
 	mbi_compose_msi_msg(data, msg);
···
 
 static int mbi_allocate_domains(struct irq_domain *parent)
 {
-	struct irq_domain *nexus_domain, *plat_domain;
+	struct irq_domain *nexus_domain, *pci_domain, *plat_domain;
+	int err;
 
 	nexus_domain = irq_domain_create_tree(parent->fwnode,
 					      &mbi_domain_ops, NULL);
···
 	irq_domain_update_bus_token(nexus_domain, DOMAIN_BUS_NEXUS);
 	nexus_domain->parent = parent;
 
+	err = mbi_allocate_pci_domain(nexus_domain, &pci_domain);
+
 	plat_domain = platform_msi_create_irq_domain(parent->fwnode,
 						     &mbi_pmsi_domain_info,
 						     nexus_domain);
 
-	if (!plat_domain) {
-		irq_domain_remove(plat_domain);
+	if (err || !plat_domain) {
+		if (plat_domain)
+			irq_domain_remove(plat_domain);
+		if (pci_domain)
+			irq_domain_remove(pci_domain);
 		irq_domain_remove(nexus_domain);
 		return -ENOMEM;
 	}