[PATCH v4 8/9] PCI/MSI: Introduce pci_get_msix_vec_count() interface

[Alexander Gordeev <agordeev@redhat.com>]

This update is needed to create a consistent MSI-X counterpart
for pci_get_msi_vec_count() MSI interface. Device drivers can
use this function to obtain maximum number of MSI-X interrupts
the device supports and i.e. use that number in a following call
to pci_enable_msix() interface.

Interface pci_get_msix_vec_count() supersedes pci_msix_table_size()
function and returns a negative errno if device does not support
MSI-X interrupts. After this update callers must always check the
returned value.

The only user of pci_msix_table_size() function was PCI-Express
port driver, which is also updated by this change.

Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Reviewed-by: Tejun Heo <tj@kernel.org>
---
 Documentation/PCI/MSI-HOWTO.txt |   13 +++++++++++++
 drivers/pci/msi.c               |   18 +++++++++++++-----
 drivers/pci/pcie/portdrv_core.c |    7 ++++---
 include/linux/pci.h             |    6 +++---
 4 files changed, 33 insertions(+), 11 deletions(-)

diff --git a/Documentation/PCI/MSI-HOWTO.txt b/Documentation/PCI/MSI-HOWTO.txt
index 8d35d62..7d19656 100644
--- a/Documentation/PCI/MSI-HOWTO.txt
+++ b/Documentation/PCI/MSI-HOWTO.txt
@@ -243,6 +243,19 @@ MSI-X Table.  This address is mapped by the PCI subsystem, and should not
 be accessed directly by the device driver.  If the driver wishes to
 mask or unmask an interrupt, it should call disable_irq() / enable_irq().
 
+4.3.4 pci_get_msix_vec_count
+
+int pci_get_msix_vec_count(struct pci_dev *dev)
+
+This function could be used to retrieve number of entries in the device
+MSI-X table.
+
+If this function returns a negative number, it indicates the device is
+not capable of sending MSI-Xs.
+
+If this function returns a positive number, it indicates the maximum
+number of MSI-X interrupt vectors that could be allocated.
+
 4.4 Handling devices implementing both MSI and MSI-X capabilities
 
 If a device implements both MSI and MSI-X capabilities, it can
diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index de1acb9..18e877f5 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -939,19 +939,25 @@ void pci_disable_msi(struct pci_dev *dev)
 EXPORT_SYMBOL(pci_disable_msi);
 
 /**
- * pci_msix_table_size - return the number of device's MSI-X table entries
+ * pci_get_msix_vec_count - return the number of device's MSI-X table entries
  * @dev: pointer to the pci_dev data structure of MSI-X device function
- */
-int pci_msix_table_size(struct pci_dev *dev)
+
+ * This function returns the number of device's MSI-X table entries and
+ * therefore the number of MSI-X vectors device is capable to send.
+ * It returns a negative errno if the device is not capable sending MSI-X
+ * interrupts.
+ **/
+int pci_get_msix_vec_count(struct pci_dev *dev)
 {
 	u16 control;
 
 	if (!dev->msix_cap)
-		return 0;
+		return -EINVAL;
 
 	pci_read_config_word(dev, dev->msix_cap + PCI_MSIX_FLAGS, &control);
 	return msix_table_size(control);
 }
+EXPORT_SYMBOL(pci_get_msix_vec_count);
 
 /**
  * pci_enable_msix - configure device's MSI-X capability structure
@@ -980,7 +986,9 @@ int pci_enable_msix(struct pci_dev *dev, struct msix_entry *entries, int nvec)
 	if (status)
 		return status;
 
-	nr_entries = pci_msix_table_size(dev);
+	nr_entries = pci_get_msix_vec_count(dev);
+	if (nr_entries < 0)
+		return nr_entries;
 	if (nvec > nr_entries)
 		return nr_entries;
 
diff --git a/drivers/pci/pcie/portdrv_core.c b/drivers/pci/pcie/portdrv_core.c
index ce9d9ae..8ba9db0 100644
--- a/drivers/pci/pcie/portdrv_core.c
+++ b/drivers/pci/pcie/portdrv_core.c
@@ -79,9 +79,10 @@ static int pcie_port_enable_msix(struct pci_dev *dev, int *vectors, int mask)
 	u16 reg16;
 	u32 reg32;
 
-	nr_entries = pci_msix_table_size(dev);
-	if (!nr_entries)
-		return -EINVAL;
+	nr_entries = pci_get_msix_vec_count(dev);
+	if (nr_entries < 0)
+		return nr_entries;
+	BUG_ON(!nr_entries);
 	if (nr_entries > PCIE_PORT_MAX_MSIX_ENTRIES)
 		nr_entries = PCIE_PORT_MAX_MSIX_ENTRIES;
 
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 8d9eb6b..7941f06 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1169,9 +1169,9 @@ static inline void pci_msi_shutdown(struct pci_dev *dev)
 static inline void pci_disable_msi(struct pci_dev *dev)
 { }
 
-static inline int pci_msix_table_size(struct pci_dev *dev)
+static inline int pci_get_msix_vec_count(struct pci_dev *dev)
 {
-	return 0;
+	return -ENOSYS;
 }
 static inline int pci_enable_msix(struct pci_dev *dev,
 				  struct msix_entry *entries, int nvec)
@@ -1198,7 +1198,7 @@ int pci_get_msi_vec_count(struct pci_dev *dev);
 int pci_enable_msi_block(struct pci_dev *dev, int nvec);
 void pci_msi_shutdown(struct pci_dev *dev);
 void pci_disable_msi(struct pci_dev *dev);
-int pci_msix_table_size(struct pci_dev *dev);
+int pci_get_msix_vec_count(struct pci_dev *dev);
 int pci_enable_msix(struct pci_dev *dev, struct msix_entry *entries, int nvec);
 void pci_msix_shutdown(struct pci_dev *dev);
 void pci_disable_msix(struct pci_dev *dev);
-- 
1.7.7.6