Add Documentation for the newly introduced dynamic allocation and deallocation of MSI-X vectors. Cc: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx> Cc: Ashok Raj <ashok.raj@xxxxxxxxx> Signed-off-by: Megha Dey <megha.dey@xxxxxxxxxxxxxxx> --- Documentation/PCI/MSI-HOWTO.txt | 38 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) diff --git a/Documentation/PCI/MSI-HOWTO.txt b/Documentation/PCI/MSI-HOWTO.txt index 618e13d..5f6daf4 100644 --- a/Documentation/PCI/MSI-HOWTO.txt +++ b/Documentation/PCI/MSI-HOWTO.txt @@ -156,6 +156,44 @@ the driver can specify that only MSI or MSI-X is acceptable: if (nvec < 0) goto out_err; +4.2.1 Dynamic MSI-X Allocation: + +The pci_alloc_irq_vectors() API is a one-shot method to allocate MSI resources +i.e. they cannot be called multiple times. In order to allocate MSI-X vectors +post probe phase, multiple times, use the following API: + + int pci_alloc_irq_vectors_dyn(struct pci_dev *dev, unsigned int min_vecs, + unsigned int max_vecs, unsigned int flags, int *group_id); + +This API allocates up to max_vecs interrupt vectors for a PCI device. It returns +the number of vectors allocated or a negative error. If the device has a +requirement for a minimum number of vectors the driver can pass a min_vecs +argument set to this limit, and the PCI core will return -ENOSPC if it can't +meet the minimum number of vectors. This API is only to be used for MSI-X vectors. + +A group ID pointer is passed which gets populated by this function. A unique +group_id will associated with all the MSI-X vectors allocated each time this +function is called: + + int group_id; + nvec = pci_alloc_irq_vectors_dyn(pdev, minvecs, maxvecs, + flags | PCI_IRQ_MSIX, &group_id); + if (nvec < 0) + goto out_err; + +To get the Linux IRQ numbers to pass to request_irq() and free_irq(), use the +following function: + + int pci_irq_vec_grp(struct pci_dev *dev, unsigned int nr, unsigned int group_id); + +In order to free the MSI-X resources associated with a particular group, use +the following function: + + int pci_free_irq_vectors_grp(struct pci_dev *dev, int group_id); + +For example, to delete the group allocated with the pci_alloc_irq_vectors_dyn(), + nvec = pci_free_irq_vectors_grp(pdev, group_id); + 4.3 Legacy APIs The following old APIs to enable and disable MSI or MSI-X interrupts should -- 2.7.4
