xref: /kernel/linux/linux-6.6/Documentation/devicetree/bindings/powerpc/fsl/msi-pic.txt

* Freescale MSI interrupt controller

Required properties:
- compatible : compatible list, may contain one or two entries
  The first is "fsl,CHIP-msi", where CHIP is the processor(mpc8610, mpc8572,
  etc.) and the second is "fsl,mpic-msi" or "fsl,ipic-msi" or
  "fsl,mpic-msi-v4.3" depending on the parent type and version. If mpic
  version is 4.3, the number of MSI registers is increased to 16, MSIIR1 is
  provided to access these 16 registers, and compatible "fsl,mpic-msi-v4.3"
  should be used. The first entry is optional; the second entry is
  required.

- reg : It may contain one or two regions. The first region should contain
  the address and the length of the shared message interrupt register set.
  The second region should contain the address of aliased MSIIR or MSIIR1
  register for platforms that have such an alias, if using MSIIR1, the second
  region must be added because different MSI group has different MSIIR1 offset.

- interrupts : each one of the interrupts here is one entry per 32 MSIs,
  and routed to the host interrupt controller. the interrupts should
  be set as edge sensitive.  If msi-available-ranges is present, only
  the interrupts that correspond to available ranges shall be present.

Optional properties:
- msi-available-ranges: use <start count> style section to define which
  msi interrupt can be used in the 256 msi interrupts. This property is
  optional, without this, all the MSI interrupts can be used.
  Each available range must begin and end on a multiple of 32 (i.e.
  no splitting an individual MSI register or the associated PIC interrupt).
  MPIC v4.3 does not support this property because the 32 interrupts of an
  individual register are not continuous when using MSIIR1.

- msi-address-64: 64-bit PCI address of the MSIIR register. The MSIIR register
  is used for MSI messaging.  The address of MSIIR in PCI address space is
  the MSI message address.

  This property may be used in virtualized environments where the hypervisor
  has created an alternate mapping for the MSIR block.  See below for an
  explanation.


Example:
	msi@41600 {
		compatible = "fsl,mpc8610-msi", "fsl,mpic-msi";
		reg = <0x41600 0x80>;
		msi-available-ranges = <0 0x100>;
		interrupts = <
			0xe0 0
			0xe1 0
			0xe2 0
			0xe3 0
			0xe4 0
			0xe5 0
			0xe6 0
			0xe7 0>;
		interrupt-parent = <&mpic>;
	};

	msi@41600 {
		compatible = "fsl,mpic-msi-v4.3";
		reg = <0x41600 0x200 0x44148 4>;
		interrupts = <
			0xe0 0 0 0
			0xe1 0 0 0
			0xe2 0 0 0
			0xe3 0 0 0
			0xe4 0 0 0
			0xe5 0 0 0
			0xe6 0 0 0
			0xe7 0 0 0
			0x100 0 0 0
			0x101 0 0 0
			0x102 0 0 0
			0x103 0 0 0
			0x104 0 0 0
			0x105 0 0 0
			0x106 0 0 0
			0x107 0 0 0>;
	};

The Freescale hypervisor and msi-address-64
-------------------------------------------
Normally, PCI devices have access to all of CCSR via an ATMU mapping.  The
Freescale MSI driver calculates the address of MSIIR (in the MSI register
block) and sets that address as the MSI message address.

In a virtualized environment, the hypervisor may need to create an IOMMU
mapping for MSIIR.  The Freescale ePAPR hypervisor has this requirement
because of hardware limitations of the Peripheral Access Management Unit
(PAMU), which is currently the only IOMMU that the hypervisor supports.
The ATMU is programmed with the guest physical address, and the PAMU
intercepts transactions and reroutes them to the true physical address.

In the PAMU, each PCI controller is given only one primary window.  The
PAMU restricts DMA operations so that they can only occur within a window.
Because PCI devices must be able to DMA to memory, the primary window must
be used to cover all of the guest's memory space.

PAMU primary windows can be divided into 256 subwindows, and each
subwindow can have its own address mapping ("guest physical" to "true
physical").  However, each subwindow has to have the same alignment, which
means they cannot be located at just any address.  Because of these
restrictions, it is usually impossible to create a 4KB subwindow that
covers MSIIR where it's normally located.

Therefore, the hypervisor has to create a subwindow inside the same
primary window used for memory, but mapped to the MSIR block (where MSIIR
lives).  The first subwindow after the end of guest memory is used for
this.  The address specified in the msi-address-64 property is the PCI
address of MSIIR.  The hypervisor configures the PAMU to map that address to
the true physical address of MSIIR.