[PATCH] PCI: Test INTx masking during enumeration, not at run-time

[Piotr Gregor]

The test for INTx masking via PCI_COMMAND_INTX_DISABLE performed in
pci_intx_mask_supported() should be done before the device can be used.
This is to avoid writing PCI_COMMAND while the driver owns the device, in
case that has any effect on MSI/MSI-X interrupts.

Move the content of pci_intx_mask_supported() to pci_intx_mask_broken() and
call it from pci_setup_device().

The test result can be queried at any time later using the same
pci_intx_mask_supported() interface as before (though with changed
implementation), so callers (uio, vfio) should be unaffected.

Signed-off-by: Piotr Gregor <piotrgregor@xxxxxxxxxxx>
[bhelgaas: changelog, remove quirk check, remove locking, move
dev->broken_intx_masking assignment to caller]
Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Reviewed-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
 drivers/pci/pci.c   | 42 +-----------------------------------------
 drivers/pci/probe.c | 30 ++++++++++++++++++++++++++++++
 include/linux/pci.h | 12 ++++++++++--
 3 files changed, 41 insertions(+), 43 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b01bd5b..7c4e1aa 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3708,46 +3708,6 @@ void pci_intx(struct pci_dev *pdev, int enable)
 }
 EXPORT_SYMBOL_GPL(pci_intx);
 
-/**
- * pci_intx_mask_supported - probe for INTx masking support
- * @dev: the PCI device to operate on
- *
- * Check if the device dev support INTx masking via the config space
- * command word.
- */
-bool pci_intx_mask_supported(struct pci_dev *dev)
-{
-	bool mask_supported = false;
-	u16 orig, new;
-
-	if (dev->broken_intx_masking)
-		return false;
-
-	pci_cfg_access_lock(dev);
-
-	pci_read_config_word(dev, PCI_COMMAND, &orig);
-	pci_write_config_word(dev, PCI_COMMAND,
-			      orig ^ PCI_COMMAND_INTX_DISABLE);
-	pci_read_config_word(dev, PCI_COMMAND, &new);
-
-	/*
-	 * There's no way to protect against hardware bugs or detect them
-	 * reliably, but as long as we know what the value should be, let's
-	 * go ahead and check it.
-	 */
-	if ((new ^ orig) & ~PCI_COMMAND_INTX_DISABLE) {
-		dev_err(&dev->dev, "Command register changed from 0x%x to 0x%x: driver or hardware bug?\n",
-			orig, new);
-	} else if ((new ^ orig) & PCI_COMMAND_INTX_DISABLE) {
-		mask_supported = true;
-		pci_write_config_word(dev, PCI_COMMAND, orig);
-	}
-
-	pci_cfg_access_unlock(dev);
-	return mask_supported;
-}
-EXPORT_SYMBOL_GPL(pci_intx_mask_supported);
-
 static bool pci_check_and_set_intx_mask(struct pci_dev *dev, bool mask)
 {
 	struct pci_bus *bus = dev->bus;
@@ -3798,7 +3758,7 @@ static bool pci_check_and_set_intx_mask(struct pci_dev *dev, bool mask)
  * @dev: the PCI device to operate on
  *
  * Check if the device dev has its INTx line asserted, mask it and
- * return true in that case. False is returned if not interrupt was
+ * return true in that case. False is returned if no interrupt was
  * pending.
  */
 bool pci_check_and_mask_intx(struct pci_dev *dev)
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 19c8950..e2c2650 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1330,6 +1330,34 @@ static void pci_msi_setup_pci_dev(struct pci_dev *dev)
 }
 
 /**
+ * pci_intx_mask_broken - test PCI_COMMAND_INTX_DISABLE writability
+ * @dev: PCI device
+ *
+ * Test whether PCI_COMMAND_INTX_DISABLE is writable for @dev.  Check this
+ * at enumeration-time to avoid modifying PCI_COMMAND at run-time.
+ */
+static int pci_intx_mask_broken(struct pci_dev *dev)
+{
+	u16 orig, toggle, new;
+
+	pci_read_config_word(dev, PCI_COMMAND, &orig);
+	toggle = orig ^ PCI_COMMAND_INTX_DISABLE;
+	pci_write_config_word(dev, PCI_COMMAND, toggle);
+	pci_read_config_word(dev, PCI_COMMAND, &new);
+
+	pci_write_config_word(dev, PCI_COMMAND, orig);
+
+	/*
+	 * PCI_COMMAND_INTX_DISABLE was reserved and read-only prior to PCI
+	 * r2.3, so strictly speaking, a device is not *broken* if it's not
+	 * writable.
+	 */
+	if (new != toggle)
+		return 1;
+	return 0;
+}
+
+/**
  * pci_setup_device - fill in class and map information of a device
  * @dev: the device structure to fill
  *
@@ -1399,6 +1427,8 @@ int pci_setup_device(struct pci_dev *dev)
 		}
 	}
 
+	dev->broken_intx_masking = pci_intx_mask_broken(dev);
+
 	switch (dev->hdr_type) {		    /* header type */
 	case PCI_HEADER_TYPE_NORMAL:		    /* standard header */
 		if (class == PCI_CLASS_BRIDGE_PCI)
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 33c2b0b..4f0613d 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -366,7 +366,7 @@ struct pci_dev {
 	unsigned int	is_thunderbolt:1; /* Thunderbolt controller */
 	unsigned int    __aer_firmware_first_valid:1;
 	unsigned int	__aer_firmware_first:1;
-	unsigned int	broken_intx_masking:1;
+	unsigned int	broken_intx_masking:1; /* INTx masking can't be used */
 	unsigned int	io_window_1k:1;	/* Intel P2P bridge 1K I/O windows */
 	unsigned int	irq_managed:1;
 	unsigned int	has_secondary_link:1;
@@ -1003,6 +1003,15 @@ int __must_check pci_reenable_device(struct pci_dev *);
 int __must_check pcim_enable_device(struct pci_dev *pdev);
 void pcim_pin_device(struct pci_dev *pdev);
 
+static inline bool pci_intx_mask_supported(struct pci_dev *pdev)
+{
+	/*
+	 * INTx masking is supported if PCI_COMMAND_INTX_DISABLE is
+	 * writable and no quirk has marked the feature broken.
+	 */
+	return !pdev->broken_intx_masking;
+}
+
 static inline int pci_is_enabled(struct pci_dev *pdev)
 {
 	return (atomic_read(&pdev->enable_cnt) > 0);
@@ -1026,7 +1035,6 @@ int __must_check pci_set_mwi(struct pci_dev *dev);
 int pci_try_set_mwi(struct pci_dev *dev);
 void pci_clear_mwi(struct pci_dev *dev);
 void pci_intx(struct pci_dev *dev, int enable);
-bool pci_intx_mask_supported(struct pci_dev *dev);
 bool pci_check_and_mask_intx(struct pci_dev *dev);
 bool pci_check_and_unmask_intx(struct pci_dev *dev);
 int pci_wait_for_pending(struct pci_dev *dev, int pos, u16 mask);
-- 
2.1.4


--GvXjxJ+pjyke8COw--