-table/MSI-X PBA. A device driver is prohibited from requesting the MMIO
-address space of the MSI-X table/MSI-X PBA. Otherwise, the PCI subsystem
-will fail enabling MSI-X on its hardware device when it calls the function
-pci_enable_msix().
-
-5.3.2 Handling MSI-X allocation
-
-Determining the number of MSI-X vectors allocated to a function is
-dependent on the number of MSI capable devices and MSI-X capable
-devices populated in the system. The policy of allocating MSI-X
-vectors to a function is defined as the following:
-
-#of MSI-X vectors allocated to a function = (x - y)/z where
-
-x = The number of available PCI vector resources by the time
- the device driver calls pci_enable_msix(). The PCI vector
- resources is the sum of the number of unassigned vectors
- (new) and the number of released vectors when any MSI/MSI-X
- device driver switches its hardware device back to a legacy
- mode or is hot-removed. The number of unassigned vectors
- may exclude some vectors reserved, as defined in parameter
- NR_HP_RESERVED_VECTORS, for the case where the system is
- capable of supporting hot-add/hot-remove operations. Users
- may change the value defined in NR_HR_RESERVED_VECTORS to
- meet their specific needs.
-
-y = The number of MSI capable devices populated in the system.
- This policy ensures that each MSI capable device has its
- vector reserved to avoid the case where some MSI-X capable
- drivers may attempt to claim all available vector resources.
-
-z = The number of MSI-X capable devices populated in the system.
- This policy ensures that maximum (x - y) is distributed
- evenly among MSI-X capable devices.
-
-Note that the PCI subsystem scans y and z during a bus enumeration.
-When the PCI subsystem completes configuring MSI/MSI-X capability
-structure of a device as requested by its device driver, y/z is
-decremented accordingly.
-
-5.3.3 Handling MSI-X shortages
-
-For the case where fewer MSI-X vectors are allocated to a function
-than requested, the function pci_enable_msix() will return the
-maximum number of MSI-X vectors available to the caller. A device
-driver may re-send its request with fewer or equal vectors indicated
-in the return. For example, if a device driver requests 5 vectors, but
-the number of available vectors is 3 vectors, a value of 3 will be
-returned as a result of pci_enable_msix() call. A function could be
-designed for its driver to use only 3 MSI-X table entries as
-different combinations as ABC--, A-B-C, A--CB, etc. Note that this
-patch does not support multiple entries with the same vector. Such
-attempt by a device driver to use 5 MSI-X table entries with 3 vectors
-as ABBCC, AABCC, BCCBA, etc will result as a failure by the function
-pci_enable_msix(). Below are the reasons why supporting multiple
-entries with the same vector is an undesirable solution.
-
- - The PCI subsystem cannot determine the entry that
- generated the message to mask/unmask MSI while handling
- software driver ISR. Attempting to walk through all MSI-X
- table entries (2048 max) to mask/unmask any match vector
- is an undesirable solution.
-
- - Walking through all MSI-X table entries (2048 max) to handle
- SMP affinity of any match vector is an undesirable solution.
-
-5.3.4 API pci_enable_msix
projects / linux-2.6-omap-h63xx.git / blobdiff