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Legacy PCI INTx interrupts are represented in the PCI_INTERRUPT_PIN
register using the range 1-4, which matches our enum pci_interrupt_pin.
This is however not ideal for an IRQ domain, where with 4 interrupts we
would ideally have a domain of size 4 & hwirq numbers in the range 0-3.
Different PCI host controller drivers have handled this in different ways.
Of those under drivers/pci/ which register an INTx IRQ domain, we have:
- pcie-altera uses the range 1-4 in device trees and an IRQ domain of
size 5 to cover that range, with entry 0 wasted.
- pcie-xilinx & pcie-xilinx-nwl use the range 1-4 in device trees but
register an IRQ domain of size 4, which doesn't cover the hwirq=4/INTD
case leading to that interrupt being broken.
- pci-ftpci100 & pci-aardvark use the range 0-3 in both device trees & as
hwirq numbering in the driver & IRQ domain.
In order to introduce some level of consistency in at least the hwirq
numbering used by the drivers & IRQ domains, this patch introduces a new
pci_irqd_intx_xlate() helper function which drivers using the 1-4 range in
device trees can assign as the xlate callback for their INTx IRQ domain.
This translates the 1-4 range into a 0-3 range, allowing us to use an IRQ
domain of size 4 & avoid a wasted entry. Further patches will make use of
this in drivers to allow them to use an IRQ domain of size 4 for legacy
INTx interrupts without breaking INTD.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.