[PATCH] PCI PCIe portdrv: Fix allocation of interrupts (rev. 3)

[Rafael J. Wysocki]

Hi,

The patch below fixes the problem with MSI-X vectors allocation by the PCIe
port driver.  It applies on top of the series of PCIe port driver cleanups and
bug fixes I've just sent.

Please review.

Thanks,
Rafael

---
Subject: PCI PCIe portdrv: Fix allocation of interrupts (rev. 3)
From: Rafael J. Wysocki <rjw@xxxxxxx>

If MSI-X interrupt mode is used by the PCI Express port driver, too
many vectors are allocated and it is not ensured that the right
vectors will be used for the right services.  Namely, the PCI Express
specification states that both PCI Express native PME and PCI Express
hotplug will always use the same MSI or MSI-X message for signalling
interrupts, which implies that the same vector will be used by both
of them.  Also, the VC service does not use interrupts at all.
Moreover, is not clear which of the vectors allocated by
pci_enable_msix() will be used for PME and hotplug and which of them
will be used for AER if all of these services are configured.

For these reasons, rework the allocation of interrupts for PCI
Express ports so that at most two vectors are allocated and ensure
that the right vector will be used for the right purpose.

Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
---
 drivers/pci/pcie/portdrv.h      |    2 
 drivers/pci/pcie/portdrv_core.c |  142 +++++++++++++++++++++++++++++-----------
 include/linux/pcieport_if.h     |   12 ++-
 3 files changed, 114 insertions(+), 42 deletions(-)

Index: linux-2.6/drivers/pci/pcie/portdrv_core.c
===================================================================
--- linux-2.6.orig/drivers/pci/pcie/portdrv_core.c
+++ linux-2.6/drivers/pci/pcie/portdrv_core.c
@@ -31,6 +31,72 @@ static void release_pcie_device(struct d
 }
 
 /**
+ * pcie_port_enable_msix - try to set up MSI-X as interrupt mode for given port
+ * @dev: PCI Express port to handle
+ * @vectors: Array of interrupt vectors to populate
+ * @nvec: Number of interrupt vectors to allocate
+ *
+ * Return value: 0 on success, error code on failure
+ */
+static int pcie_port_enable_msix(struct pci_dev *dev, int *vectors, int nvec)
+{
+	struct msix_entry msix_entries[PCIE_PORT_DEVICE_MAXINTERRUPTS] = {
+		{ 0, },
+	};
+	int status, pos, i;
+	u16 reg16;
+	u32 reg32;
+
+	for (i = 0; i < nvec; i++)
+		msix_entries[i].entry = i;
+
+	status = pci_enable_msix(dev, msix_entries, nvec);
+	if (status)
+		return status;
+
+	/*
+	 * The code below follows the PCI Express Base Specification 2.0 clearly
+	 * stating in Section 6.1.6 that "PME and Hot-Plug Event interrupts
+	 * (when both are implemented) always share the same MSI or MSI-X
+	 * vector, as indicated by the Interrupt Message Number field in the PCI
+	 * Express Capabilities register", where according to Section 7.8.2 of
+	 * the Specification "For MSI-X, the value in this field indicates which
+	 * MSI-X Table entry is used to generate the interrupt message."
+	 */
+	pos = pci_find_capability(dev, PCI_CAP_ID_EXP);
+	pci_read_config_word(dev, pos + PCIE_CAPABILITIES_REG, &reg16);
+	i = (reg16 >> 9) & PCIE_PORT_MSI_VECTOR_MASK;
+	if (i >= nvec) {
+		goto Error;
+	} else {
+		vectors[PCIE_PORT_SERVICE_PME_SHIFT] = msix_entries[i].vector;
+		vectors[PCIE_PORT_SERVICE_HP_SHIFT] = msix_entries[i].vector;
+	}
+
+	/*
+	 * The code below follows Section 7.10.10 of the PCI Express Base
+	 * Specification 2.0 stating that bits 31-27 of the Root Error Status
+	 * Register contain a value indicating which of the MSI/MSI-X vectors
+	 * assigned to the port is going to be used for AER, where "For MSI-X,
+	 * the value in this register indicates which MSI-X Table entry is used
+	 * to generate the interrupt message."
+	 */
+	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ERR);
+	pci_read_config_dword(dev, pos + PCI_ERR_ROOT_STATUS, &reg32);
+	i = (reg32 >> 27) & PCIE_PORT_MSI_VECTOR_MASK;
+	if (i >= nvec)
+		goto Error;
+	else
+		vectors[PCIE_PORT_SERVICE_AER_SHIFT] = msix_entries[i].vector;
+
+	return 0;
+
+ Error:
+	pci_disable_msix(dev);
+	return -EIO;
+}
+
+/**
  * assign_interrupt_mode - choose interrupt mode for PCI Express port services
  *                         (INTx, MSI-X, MSI) and set up vectors
  * @dev: PCI Express port to handle
@@ -42,49 +108,49 @@ static void release_pcie_device(struct d
 static int assign_interrupt_mode(struct pci_dev *dev, int *vectors, int mask)
 {
 	struct pcie_port_data *port_data = pci_get_drvdata(dev);
-	int i, pos, nvec, status = -EINVAL;
-	int interrupt_mode = PCIE_PORT_NO_IRQ;
+	int nvec, irq, interrupt_mode = PCIE_PORT_NO_IRQ;
+	int i;
 
-	/* Set INTx as default */
-	for (i = 0, nvec = 0; i < PCIE_PORT_DEVICE_MAXSERVICES; i++) {
-		if (mask & (1 << i)) 
-			nvec++;
-		vectors[i] = dev->irq;
-	}
-	if (dev->pin)
-		interrupt_mode = PCIE_PORT_INTx_MODE;
+	/*
+	 * Determine the number of vectors to allocate.
+	 *
+	 * According to the PCI Express specification both PME and PCI Express
+	 * hotplug always use the same interrupt vector, while AER can use
+	 * a different one.
+	 */
+	nvec = 0;
+	if (mask & (PCIE_PORT_SERVICE_PME | PCIE_PORT_SERVICE_HP))
+		nvec++;
+	if (mask & PCIE_PORT_SERVICE_AER)
+		nvec++;
+	if (!nvec)
+		return PCIE_PORT_NO_IRQ;
 
 	/* Check MSI quirk */
 	if (port_data->port_type == PCIE_RC_PORT && pcie_mch_quirk)
-		return interrupt_mode;
+		goto Fallback;
+
+	/* For nvec > 1 use MSI-X if supported */
+	if (nvec > 1 && !pcie_port_enable_msix(dev, vectors, nvec)) {
+		interrupt_mode = PCIE_PORT_MSIX_MODE;
+		goto Exit;
+	}
+
+	/* We're not going to use MSI-X, so try MSI and fall back to INTx */
+	if (!pci_enable_msi(dev))
+		interrupt_mode = PCIE_PORT_MSI_MODE;
+
+ Fallback:
+	if (interrupt_mode == PCIE_PORT_NO_IRQ && dev->pin)
+		interrupt_mode = PCIE_PORT_INTx_MODE;
+
+	irq = interrupt_mode != PCIE_PORT_NO_IRQ ? dev->irq : -1;
+	for (i = 0; i < PCIE_PORT_DEVICE_MAXSERVICES; i++)
+		vectors[i] = irq;
+
+ Exit:
+	vectors[PCIE_PORT_SERVICE_VC_SHIFT] = -1;
 
-	/* Select MSI-X over MSI if supported */		
-	pos = pci_find_capability(dev, PCI_CAP_ID_MSIX);
-	if (pos) {
-		struct msix_entry msix_entries[PCIE_PORT_DEVICE_MAXSERVICES] = 
-			{{0, 0}, {0, 1}, {0, 2}, {0, 3}};
-		status = pci_enable_msix(dev, msix_entries, nvec);
-		if (!status) {
-			int j = 0;
-
-			interrupt_mode = PCIE_PORT_MSIX_MODE;
-			for (i = 0; i < PCIE_PORT_DEVICE_MAXSERVICES; i++) {
-				if (mask & (1 << i)) 
-					vectors[i] = msix_entries[j++].vector;
-			}
-		}
-	} 
-	if (status) {
-		pos = pci_find_capability(dev, PCI_CAP_ID_MSI);
-		if (pos) {
-			status = pci_enable_msi(dev);
-			if (!status) {
-				interrupt_mode = PCIE_PORT_MSI_MODE;
-				for (i = 0;i < PCIE_PORT_DEVICE_MAXSERVICES;i++)
-					vectors[i] = dev->irq;
-			}
-		}
-	} 
 	return interrupt_mode;
 }
 
Index: linux-2.6/include/linux/pcieport_if.h
===================================================================
--- linux-2.6.orig/include/linux/pcieport_if.h
+++ linux-2.6/include/linux/pcieport_if.h
@@ -16,10 +16,14 @@
 #define PCIE_ANY_PORT			7
 
 /* Service Type */
-#define PCIE_PORT_SERVICE_PME		1	/* Power Management Event */
-#define PCIE_PORT_SERVICE_AER		2	/* Advanced Error Reporting */
-#define PCIE_PORT_SERVICE_HP		4	/* Native Hotplug */
-#define PCIE_PORT_SERVICE_VC		8	/* Virtual Channel */
+#define PCIE_PORT_SERVICE_PME_SHIFT	0	/* Power Management Event */
+#define PCIE_PORT_SERVICE_PME		(1 << PCIE_PORT_SERVICE_PME_SHIFT)
+#define PCIE_PORT_SERVICE_AER_SHIFT	1	/* Advanced Error Reporting */
+#define PCIE_PORT_SERVICE_AER		(1 << PCIE_PORT_SERVICE_AER_SHIFT)
+#define PCIE_PORT_SERVICE_HP_SHIFT	2	/* Native Hotplug */
+#define PCIE_PORT_SERVICE_HP		(1 << PCIE_PORT_SERVICE_HP_SHIFT)
+#define PCIE_PORT_SERVICE_VC_SHIFT	3	/* Virtual Channel */
+#define PCIE_PORT_SERVICE_VC		(1 << PCIE_PORT_SERVICE_VC_SHIFT)
 
 /* Root/Upstream/Downstream Port's Interrupt Mode */
 #define PCIE_PORT_NO_IRQ		(-1)
Index: linux-2.6/drivers/pci/pcie/portdrv.h
===================================================================
--- linux-2.6.orig/drivers/pci/pcie/portdrv.h
+++ linux-2.6/drivers/pci/pcie/portdrv.h
@@ -25,6 +25,8 @@
 #define PCIE_CAPABILITIES_REG		0x2
 #define PCIE_SLOT_CAPABILITIES_REG	0x14
 #define PCIE_PORT_DEVICE_MAXSERVICES	4
+#define PCIE_PORT_DEVICE_MAXINTERRUPTS	2
+#define PCIE_PORT_MSI_VECTOR_MASK	0x1f
 
 #define get_descriptor_id(type, service) (((type - 4) << 4) | service)
 

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/