[PATCH] cxl: Add generic MSI/MSI-X interrupt support

[Davidlohr Bueso]

Introduce a generic irq table for CXL components/features that can have
standard irq support - DOE requires dynamic vector sizing and is not
considered here.

Create an infrastructure to query the max vectors required for the CXL
device.

Signed-off-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>
---
 drivers/cxl/pci.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)

diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
index faeb5d9d7a7a..467f2d568e3e 100644
--- a/drivers/cxl/pci.c
+++ b/drivers/cxl/pci.c
@@ -428,6 +428,66 @@ static void devm_cxl_pci_create_doe(struct cxl_dev_state *cxlds)
 	}
 }
 
+/**
+ * struct cxl_irq_cap - CXL feature that is capable of receiving MSI/MSI-X irqs.
+ *
+ * @name: Name of the device generating this interrupt.
+ * @get_max_msgnum: Get the feature's largest interrupt message number.  If the
+ *		    feature does not have the Interrupt Supported bit set, then
+ *		    return -1.
+ */
+struct cxl_irq_cap {
+	const char *name;
+	int (*get_max_msgnum)(struct cxl_dev_state *cxlds);
+};
+
+static const struct cxl_irq_cap cxl_irq_cap_table[] = {
+	{ "isolation", NULL },
+	{ "pmu_overflow", NULL },
+	{ "mailbox", NULL },
+	{ "event", NULL },
+};
+
+static void cxl_pci_free_irq_vectors(void *data)
+{
+	pci_free_irq_vectors(data);
+}
+
+static int cxl_pci_alloc_irq_vectors(struct cxl_dev_state *cxlds)
+{
+	struct device *dev = cxlds->dev;
+	struct pci_dev *pdev = to_pci_dev(dev);
+	int rc, i, vectors = -1;
+
+	for (i = 0; i < ARRAY_SIZE(cxl_irq_cap_table); i++) {
+		int irq;
+
+		if (!cxl_irq_cap_table[i].get_max_msgnum)
+			continue;
+
+		irq = cxl_irq_cap_table[i].get_max_msgnum(cxlds);
+		vectors = max_t(int, irq, vectors);
+	}
+
+	if (vectors == -1)
+		return -EINVAL; /* no irq support whatsoever */
+
+	vectors++;
+	rc = pci_alloc_irq_vectors(pdev, vectors, vectors,
+				   PCI_IRQ_MSIX | PCI_IRQ_MSI);
+	if (rc < 0)
+		return rc;
+
+	if (rc != vectors) {
+		dev_err(dev, "Not enough interrupts; use polling where supported\n");
+		/* Some got allocated; clean them up */
+		cxl_pci_free_irq_vectors(pdev);
+		return -ENOSPC;
+	}
+
+	return devm_add_action_or_reset(dev, cxl_pci_free_irq_vectors, pdev);
+}
+
 static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 {
 	struct cxl_register_map map;
@@ -498,6 +558,9 @@ static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	if (IS_ERR(cxlmd))
 		return PTR_ERR(cxlmd);
 
+	/* TODO: When there are users, this return value must be checked */
+	cxl_pci_alloc_irq_vectors(cxlds);
+
 	if (resource_size(&cxlds->pmem_res) && IS_ENABLED(CONFIG_CXL_PMEM))
 		rc = devm_cxl_add_nvdimm(&pdev->dev, cxlmd);
 
-- 
2.37.3