[PATCH] PCI: Move test of INTx masking to pci_setup_device

[Piotr Gregor <piotrgregor@rsyncme.org>]

The test for INTx masking via config space command performed
in pci_intx_mask_supported should be performed before PCI device
can be used. This is to avoid reading/writing of PCI_COMMAND_INTX_DISABLE
register which may collide with MSI/MSI-X interrupts.

This patch simplifies test performed in pci_intx_mask_supported
and introduces intx_mask_support field in struct pci_dev to store
the result. The test itself is moved to pci_setup_device.
The result can be queried at any time later from the pci_dev with

static inline bool pci_is_intx_mask_supported(struct pci_dev *pdev)
{
        /*
         * INTx masking is supported if device passed INTx test
         * and it's INTx masking feature works properly.
         */
        return (pdev->intx_mask_support && !pdev->broken_intx_masking);
}

Signed-off-by: Piotr Gregor <piotrgregor@rsyncme.org>
---
 drivers/pci/pci.c             | 42 +++++++++++++++++++++++-------------------
 drivers/pci/probe.c           |  3 +++
 drivers/uio/uio_pci_generic.c |  2 +-
 drivers/vfio/pci/vfio_pci.c   |  2 +-
 include/linux/pci.h           | 10 ++++++++++
 5 files changed, 38 insertions(+), 21 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b01bd5b..bcaab9b 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3709,42 +3709,46 @@ void pci_intx(struct pci_dev *pdev, int enable)
 EXPORT_SYMBOL_GPL(pci_intx);
 
 /**
- * pci_intx_mask_supported - probe for INTx masking support
+ * pci_intx_mask_supported - probe for INTx masking support in pci_setup_device
  * @dev: the PCI device to operate on
  *
- * Check if the device dev support INTx masking via the config space
- * command word.
+ * Check if the device dev supports INTx masking via the config space
+ * command word. Executed when PCI device is setup. Result is saved
+ * in intx_mask_support field of pci_dev and should be checked
+ * with pci_is_intx_mask_supported() after PCI device has been setup
+ * to avoid reading/writing of PCI_COMMAND_INTX_DISABLE register.
  */
 bool pci_intx_mask_supported(struct pci_dev *dev)
 {
-	bool mask_supported = false;
-	u16 orig, new;
+	u16 orig, toggle, new;
 
+	/*
+	 * If device doesn't support this feature though it could pass the test.
+	 */
 	if (dev->broken_intx_masking)
 		return false;
 
 	pci_cfg_access_lock(dev);
 
+	/*
+	 * Perform the test.
+	 */
 	pci_read_config_word(dev, PCI_COMMAND, &orig);
-	pci_write_config_word(dev, PCI_COMMAND,
-			      orig ^ PCI_COMMAND_INTX_DISABLE);
+	toggle = orig ^ PCI_COMMAND_INTX_DISABLE;
+	pci_write_config_word(dev, PCI_COMMAND, toggle);
 	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.
+	 * Restore initial state.
 	 */
-	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_write_config_word(dev, PCI_COMMAND, orig);
 
 	pci_cfg_access_unlock(dev);
-	return mask_supported;
+
+	if (new == toggle)
+		return true;
+
+	return false;
 }
 EXPORT_SYMBOL_GPL(pci_intx_mask_supported);
 
@@ -3798,7 +3802,7 @@ 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..16c60ce 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1399,6 +1399,9 @@ int pci_setup_device(struct pci_dev *dev)
 		}
 	}
 
+	if (pci_intx_mask_supported(dev))
+		dev->intx_mask_support = 1;
+
 	switch (dev->hdr_type) {		    /* header type */
 	case PCI_HEADER_TYPE_NORMAL:		    /* standard header */
 		if (class == PCI_CLASS_BRIDGE_PCI)
diff --git a/drivers/uio/uio_pci_generic.c b/drivers/uio/uio_pci_generic.c
index d0b508b..8cd443c 100644
--- a/drivers/uio/uio_pci_generic.c
+++ b/drivers/uio/uio_pci_generic.c
@@ -73,7 +73,7 @@ static int probe(struct pci_dev *pdev,
 		return -ENODEV;
 	}
 
-	if (!pci_intx_mask_supported(pdev)) {
+	if (!pci_is_intx_mask_supported(pdev)) {
 		err = -ENODEV;
 		goto err_verify;
 	}
diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 324c52e..933456e 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -239,7 +239,7 @@ static int vfio_pci_enable(struct vfio_pci_device *vdev)
 			vdev->nointx = true;
 			pci_intx(pdev, 0);
 		} else
-			vdev->pci_2_3 = pci_intx_mask_supported(pdev);
+			vdev->pci_2_3 = pci_is_intx_mask_supported(pdev);
 	}
 
 	pci_read_config_word(pdev, PCI_COMMAND, &cmd);
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 33c2b0b..0fbd278 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -367,6 +367,7 @@ struct pci_dev {
 	unsigned int    __aer_firmware_first_valid:1;
 	unsigned int	__aer_firmware_first:1;
 	unsigned int	broken_intx_masking:1;
+	unsigned int	intx_mask_support:1;	/* INTx masking is supported */
 	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 +1004,15 @@ 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_is_intx_mask_supported(struct pci_dev *pdev)
+{
+	/*
+	 * INTx masking is supported if device passed INTx test and it's INTx
+	 * masking feature works properly.
+	 */
+	return (pdev->intx_mask_support && !pdev->broken_intx_masking);
+}
+
 static inline int pci_is_enabled(struct pci_dev *pdev)
 {
 	return (atomic_read(&pdev->enable_cnt) > 0);
-- 
2.1.4