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author | Matthew Wilcox <willy@linux.intel.com> | 2009-03-17 08:54:10 -0400 |
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committer | Jesse Barnes <jbarnes@virtuousgeek.org> | 2009-03-20 10:48:14 -0700 |
commit | 1c8d7b0a562da06d3ebe83f01b1ed553205d1ae4 (patch) | |
tree | 79c84432f5aed5a08b3bef262a10d933daae6a9b /Documentation/PCI/MSI-HOWTO.txt | |
parent | f2440d9acbe866b917b16cc0f927366341ce9215 (diff) | |
download | linux-1c8d7b0a562da06d3ebe83f01b1ed553205d1ae4.tar.bz2 |
PCI MSI: Add support for multiple MSI
Add the new API pci_enable_msi_block() to allow drivers to
request multiple MSI and reimplement pci_enable_msi in terms of
pci_enable_msi_block. Ensure that the architecture back ends don't
have to know about multiple MSI.
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Diffstat (limited to 'Documentation/PCI/MSI-HOWTO.txt')
-rw-r--r-- | Documentation/PCI/MSI-HOWTO.txt | 45 |
1 files changed, 39 insertions, 6 deletions
diff --git a/Documentation/PCI/MSI-HOWTO.txt b/Documentation/PCI/MSI-HOWTO.txt index 1c02431f1d1a..9494f6dc38eb 100644 --- a/Documentation/PCI/MSI-HOWTO.txt +++ b/Documentation/PCI/MSI-HOWTO.txt @@ -94,15 +94,48 @@ This function should be called before the driver calls request_irq() since enabling MSIs disables the pin-based IRQ and the driver will not receive interrupts on the old interrupt. -4.2.2 pci_disable_msi +4.2.2 pci_enable_msi_block + +int pci_enable_msi_block(struct pci_dev *dev, int count) + +This variation on the above call allows a device driver to request multiple +MSIs. The MSI specification only allows interrupts to be allocated in +powers of two, up to a maximum of 2^5 (32). + +If this function returns 0, it has succeeded in allocating at least as many +interrupts as the driver requested (it may have allocated more in order +to satisfy the power-of-two requirement). In this case, the function +enables MSI on this device and updates dev->irq to be the lowest of +the new interrupts assigned to it. The other interrupts assigned to +the device are in the range dev->irq to dev->irq + count - 1. + +If this function returns a negative number, it indicates an error and +the driver should not attempt to request any more MSI interrupts for +this device. If this function returns a positive number, it will be +less than 'count' and indicate the number of interrupts that could have +been allocated. In neither case will the irq value have been +updated, nor will the device have been switched into MSI mode. + +The device driver must decide what action to take if +pci_enable_msi_block() returns a value less than the number asked for. +Some devices can make use of fewer interrupts than the maximum they +request; in this case the driver should call pci_enable_msi_block() +again. Note that it is not guaranteed to succeed, even when the +'count' has been reduced to the value returned from a previous call to +pci_enable_msi_block(). This is because there are multiple constraints +on the number of vectors that can be allocated; pci_enable_msi_block() +will return as soon as it finds any constraint that doesn't allow the +call to succeed. + +4.2.3 pci_disable_msi void pci_disable_msi(struct pci_dev *dev) -This function should be used to undo the effect of pci_enable_msi(). -Calling it restores dev->irq to the pin-based interrupt number and frees -the previously allocated message signaled interrupt(s). The interrupt -may subsequently be assigned to another device, so drivers should not -cache the value of dev->irq. +This function should be used to undo the effect of pci_enable_msi() or +pci_enable_msi_block(). Calling it restores dev->irq to the pin-based +interrupt number and frees the previously allocated message signaled +interrupt(s). The interrupt may subsequently be assigned to another +device, so drivers should not cache the value of dev->irq. A device driver must always call free_irq() on the interrupt(s) for which it has called request_irq() before calling this function. |