PCI/MSI: Add pci_msi_vec_count()
Device drivers can use this interface to obtain the maximum number of MSI
interrupts the device supports and use that number, e.g., in a subsequent
call to pci_enable_msi_block().
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Tejun Heo <tj@kernel.org>
diff --git a/Documentation/PCI/MSI-HOWTO.txt b/Documentation/PCI/MSI-HOWTO.txt
index a4d174e..a8b4178 100644
--- a/Documentation/PCI/MSI-HOWTO.txt
+++ b/Documentation/PCI/MSI-HOWTO.txt
@@ -169,6 +169,21 @@
Failure to do so results in a BUG_ON(), leaving the device with
MSI enabled and thus leaking its vector.
+4.2.5 pci_msi_vec_count
+
+int pci_msi_vec_count(struct pci_dev *dev)
+
+This function could be used to retrieve the number of MSI vectors the
+device requested (via the Multiple Message Capable register). The MSI
+specification only allows the returned value to be a power of two,
+up to a maximum of 2^5 (32).
+
+If this function returns a negative number, it indicates the device is
+not capable of sending MSIs.
+
+If this function returns a positive number, it indicates the maximum
+number of MSI interrupt vectors that could be allocated.
+
4.3 Using MSI-X
The MSI-X capability is much more flexible than the MSI capability.
diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index ce0d4eb..ba6d0a9 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -843,6 +843,31 @@
}
/**
+ * pci_msi_vec_count - Return the number of MSI vectors a device can send
+ * @dev: device to report about
+ *
+ * This function returns the number of MSI vectors a device requested via
+ * Multiple Message Capable register. It returns a negative errno if the
+ * device is not capable sending MSI interrupts. Otherwise, the call succeeds
+ * and returns a power of two, up to a maximum of 2^5 (32), according to the
+ * MSI specification.
+ **/
+int pci_msi_vec_count(struct pci_dev *dev)
+{
+ int ret;
+ u16 msgctl;
+
+ if (!dev->msi_cap)
+ return -EINVAL;
+
+ pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &msgctl);
+ ret = 1 << ((msgctl & PCI_MSI_FLAGS_QMASK) >> 1);
+
+ return ret;
+}
+EXPORT_SYMBOL(pci_msi_vec_count);
+
+/**
* pci_enable_msi_block - configure device's MSI capability structure
* @dev: device to configure
* @nvec: number of interrupts to configure
@@ -858,13 +883,13 @@
int pci_enable_msi_block(struct pci_dev *dev, int nvec)
{
int status, maxvec;
- u16 msgctl;
- if (!dev->msi_cap || dev->current_state != PCI_D0)
+ if (dev->current_state != PCI_D0)
return -EINVAL;
- pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &msgctl);
- maxvec = 1 << ((msgctl & PCI_MSI_FLAGS_QMASK) >> 1);
+ maxvec = pci_msi_vec_count(dev);
+ if (maxvec < 0)
+ return maxvec;
if (nvec > maxvec)
return maxvec;
@@ -889,13 +914,13 @@
int pci_enable_msi_block_auto(struct pci_dev *dev, int *maxvec)
{
int ret, nvec;
- u16 msgctl;
- if (!dev->msi_cap || dev->current_state != PCI_D0)
+ if (dev->current_state != PCI_D0)
return -EINVAL;
- pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &msgctl);
- ret = 1 << ((msgctl & PCI_MSI_FLAGS_QMASK) >> 1);
+ ret = pci_msi_vec_count(dev);
+ if (ret < 0)
+ return ret;
if (maxvec)
*maxvec = ret;
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 7c34c39..6691de0 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1154,6 +1154,11 @@
#ifndef CONFIG_PCI_MSI
+static inline int pci_msi_vec_count(struct pci_dev *dev)
+{
+ return -ENOSYS;
+}
+
static inline int pci_enable_msi_block(struct pci_dev *dev, int nvec)
{
return -ENOSYS;
@@ -1195,6 +1200,7 @@
return 0;
}
#else
+int pci_msi_vec_count(struct pci_dev *dev);
int pci_enable_msi_block(struct pci_dev *dev, int nvec);
int pci_enable_msi_block_auto(struct pci_dev *dev, int *maxvec);
void pci_msi_shutdown(struct pci_dev *dev);