136 lines
3.8 KiB
Plaintext
136 lines
3.8 KiB
Plaintext
This document describes the generic device tree binding for MSI controllers and
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their master(s).
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Message Signaled Interrupts (MSIs) are a class of interrupts generated by a
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write to an MMIO address.
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MSIs were originally specified by PCI (and are used with PCIe), but may also be
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used with other busses, and hence a mechanism is required to relate devices on
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those busses to the MSI controllers which they are capable of using,
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potentially including additional information.
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MSIs are distinguished by some combination of:
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- The doorbell (the MMIO address written to).
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Devices may be configured by software to write to arbitrary doorbells which
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they can address. An MSI controller may feature a number of doorbells.
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- The payload (the value written to the doorbell).
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Devices may be configured to write an arbitrary payload chosen by software.
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MSI controllers may have restrictions on permitted payloads.
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- Sideband information accompanying the write.
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Typically this is neither configurable nor probeable, and depends on the path
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taken through the memory system (i.e. it is a property of the combination of
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MSI controller and device rather than a property of either in isolation).
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MSI controllers:
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================
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An MSI controller signals interrupts to a CPU when a write is made to an MMIO
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address by some master. An MSI controller may feature a number of doorbells.
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Required properties:
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--------------------
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- msi-controller: Identifies the node as an MSI controller.
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Optional properties:
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--------------------
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- #msi-cells: The number of cells in an msi-specifier, required if not zero.
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Typically this will encode information related to sideband data, and will
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not encode doorbells or payloads as these can be configured dynamically.
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The meaning of the msi-specifier is defined by the device tree binding of
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the specific MSI controller.
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MSI clients
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===========
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MSI clients are devices which generate MSIs. For each MSI they wish to
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generate, the doorbell and payload may be configured, though sideband
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information may not be configurable.
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Required properties:
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--------------------
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- msi-parent: A list of phandle + msi-specifier pairs, one for each MSI
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controller which the device is capable of using.
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This property is unordered, and MSIs may be allocated from any combination of
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MSI controllers listed in the msi-parent property.
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If a device has restrictions on the allocation of MSIs, these restrictions
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must be described with additional properties.
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When #msi-cells is non-zero, busses with an msi-parent will require
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additional properties to describe the relationship between devices on the bus
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and the set of MSIs they can potentially generate.
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Example
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=======
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/ {
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#address-cells = <1>;
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#size-cells = <1>;
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msi_a: msi-controller@a {
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reg = <0xa 0xf00>;
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compatible = "vendor-a,some-controller";
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msi-controller;
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/* No sideband data, so #msi-cells omitted */
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};
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msi_b: msi-controller@b {
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reg = <0xb 0xf00>;
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compatible = "vendor-b,another-controller";
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msi-controller;
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/* Each device has some unique ID */
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#msi-cells = <1>;
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};
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msi_c: msi-controller@c {
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reg = <0xb 0xf00>;
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compatible = "vendor-b,another-controller";
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msi-controller;
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/* Each device has some unique ID */
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#msi-cells = <1>;
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};
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dev@0 {
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reg = <0x0 0xf00>;
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compatible = "vendor-c,some-device";
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/* Can only generate MSIs to msi_a */
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msi-parent = <&msi_a>;
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};
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dev@1 {
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reg = <0x1 0xf00>;
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compatible = "vendor-c,some-device";
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/*
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* Can generate MSIs to either A or B.
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*/
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msi-parent = <&msi_a>, <&msi_b 0x17>;
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};
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dev@2 {
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reg = <0x2 0xf00>;
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compatible = "vendor-c,some-device";
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/*
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* Has different IDs at each MSI controller.
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* Can generate MSIs to all of the MSI controllers.
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*/
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msi-parent = <&msi_a>, <&msi_b 0x17>, <&msi_c 0x53>;
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};
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};
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