PCI: iproc: Support multi-MSI only on uniprocessor kernel

The interrupt affinity scheme used by this driver is incompatible with
multi-MSI as it implies moving the doorbell address to that of another MSI
group.  This isn't possible for multi-MSI, as all the MSIs must have the
same doorbell address. As such it is restricted to systems with a single
CPU.

Link: https://lore.kernel.org/r/20210622152630.40842-2-sbodomerle@gmail.com
Fixes: fc54bae ("PCI: iproc: Allow allocation of multiple MSIs")
Reported-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Sandor Bodo-Merle <sbodomerle@gmail.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Acked-by: Pali Rohár <pali@kernel.org>
Acked-by: Ray Jui <ray.jui@broadcom.com>

drivers/pci/controller/pcie-iproc-msi.c

@@ -171,7 +171,7 @@ static struct irq_chip iproc_msi_irq_chip = {
 
 static struct msi_domain_info iproc_msi_domain_info = {
 	.flags = MSI_FLAG_USE_DEF_DOM_OPS | MSI_FLAG_USE_DEF_CHIP_OPS |
-		MSI_FLAG_MULTI_PCI_MSI | MSI_FLAG_PCI_MSIX,
+		MSI_FLAG_PCI_MSIX,
 	.chip = &iproc_msi_irq_chip,
 };
 
@@ -250,6 +250,9 @@ static int iproc_msi_irq_domain_alloc(struct irq_domain *domain,
 	struct iproc_msi *msi = domain->host_data;
 	int hwirq, i;
 
+	if (msi->nr_cpus > 1 && nr_irqs > 1)
+		return -EINVAL;
+
 	mutex_lock(&msi->bitmap_lock);
 
 	/*
@@ -540,6 +543,9 @@ int iproc_msi_init(struct iproc_pcie *pcie, struct device_node *node)
 	mutex_init(&msi->bitmap_lock);
 	msi->nr_cpus = num_possible_cpus();
 
+	if (msi->nr_cpus == 1)
+		iproc_msi_domain_info.flags |=  MSI_FLAG_MULTI_PCI_MSI;
+
 	msi->nr_irqs = of_irq_count(node);
 	if (!msi->nr_irqs) {
 		dev_err(pcie->dev, "found no MSI GIC interrupt\n");