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Diffstat (limited to 'Documentation/MSI-HOWTO.txt')
| -rw-r--r-- | Documentation/MSI-HOWTO.txt | 69 |
1 files changed, 4 insertions, 65 deletions
diff --git a/Documentation/MSI-HOWTO.txt b/Documentation/MSI-HOWTO.txt index 0d8240774fc..a51f693c154 100644 --- a/Documentation/MSI-HOWTO.txt +++ b/Documentation/MSI-HOWTO.txt @@ -241,68 +241,7 @@ 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 +5.3.2 API pci_enable_msix int pci_enable_msix(struct pci_dev *dev, struct msix_entry *entries, int nvec) @@ -339,7 +278,7 @@ a failure. This failure may be a result of duplicate entries specified in second argument, or a result of no available vector, or a result of failing to initialize MSI-X table entries. -5.3.5 API pci_disable_msix +5.3.3 API pci_disable_msix void pci_disable_msix(struct pci_dev *dev) @@ -349,7 +288,7 @@ always call free_irq() on all MSI-X vectors it has done request_irq() on before calling this API. Failure to do so results in a BUG_ON() and a device will be left with MSI-X enabled and leaks its vectors. -5.3.6 MSI-X mode vs. legacy mode diagram +5.3.4 MSI-X mode vs. legacy mode diagram The below diagram shows the events which switch the interrupt mode on the MSI-X capable device function between MSI-X mode and @@ -407,7 +346,7 @@ between MSI mod MSI-X mode during a run-time. MSI/MSI-X support requires support from both system hardware and individual hardware device functions. -5.5.1 System hardware support +5.5.1 Required x86 hardware support Since the target of MSI address is the local APIC CPU, enabling MSI/MSI-X support in the Linux kernel is dependent on whether existing |