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The I/O-APIC generates an MSI cycle with address/data bits taken from its Redirection Table Entry in some combination which used to make sense, but now is just a bunch of bits which get passed through in some seemingly arbitrary order. Instead of making IRQ remapping drivers directly frob the I/OA-PIC RTE, let them just do their job and generate an MSI message. The bit swizzling to turn that MSI message into the I/O-APIC's RTE is the same in all cases, since it's a function of the I/O-APIC hardware. The IRQ remappers have no real need to get involved with that. The only slight caveat is that the I/OAPIC is interpreting some of those fields too, and it does want the 'vector' field to be unique to make EOI work. The AMD IOMMU happens to put its IRTE index in the bits that the I/O-APIC thinks are the vector field, and accommodates this requirement by reserving the first 32 indices for the I/O-APIC. The Intel IOMMU doesn't actually use the bits that the I/O-APIC thinks are the vector field, so it fills in the 'pin' value there instead. [ tglx: Replaced the unreadably macro maze with the cleaned up RTE/msi_msg bitfields and added commentry to explain the mapping magic ] Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20201024213535.443185-22-dwmw2@infradead.org
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.