Subject: Master-aware devices and sideband ID data

From: [email-masked] (Mark Rutland)
Date: Thu, 16 Jul 2015 14:34:41 +0100

Hi Will,

The below is an attempt at an MSI binding, derived from my original
example. It extends msi-parent inoto a phandle+(optional args) style
property.

I haven't yet managed to come up with a sane way of describing
the Bus-ID/BDF -> {iommu,msi}-cells translation, but this should
hopefully cover the platform device case.

For the Bus-ID translation case I'm not sure it's sane to attempt to use
msi-parent, given that the transformation description will necessarily
have to describe the parents anyway.

Thanks,
Mark.

---->8----
>>From 429dca4bba98732c492e95bdf395aa2ccc634e69 Mon Sep 17 00:00:00 2001
From: Mark Rutland <[email-masked]>
Date: Thu, 9 Jul 2015 17:53:00 +0100
Subject: [PATCH] Documentation: dt: add generic MSI bindings

Currently msi-parent is in use in a couple of drviers despite being
fairly underspecified. This patch adds a generic binding for MSIs
(including the existing msi-parent property) enabling the description of
platform devices capable of using MSIs.

This binding does not yet cover the general case. Currently the binding
does not cover the relationship between bus IDs (e.g. PCIe BDF) and
sideband data.

Signed-off-by: Mark Rutland <[email-masked]>
---
 .../bindings/interrupt-controller/msi.txt          | 135 +++++++++++++++++++++
 1 file changed, 135 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/interrupt-controller/msi.txt

diff --git a/Documentation/devicetree/bindings/interrupt-controller/msi.txt b/Documentation/devicetree/bindings/interrupt-controller/msi.txt
new file mode 100644
index 0000000..c60c034
--- /dev/null
+++ b/Documentation/devicetree/bindings/interrupt-controller/msi.txt
@@ -0,0 +1,135 @@
+This document describes the generic device tree binding for MSI controllers and
+their master(s).
+
+Message Signaled Interrupts (MSIs) are a class of interrupts generated by a
+write to an MMIO address.
+
+MSIs were originally specified by PCI (and are used with PCIe), but may also be
+used with other busses, and hence a mechanism is required to relate devices on
+those busses to the MSI controllers which they are capable of using,
+potentially including additional information.
+
+MSIs are distinguished by some combination of:
+
+- The doorbell (the MMIO address written to).
+  
+  Devices may be configured by software to write to arbitrary doorbells which
+  they can address. An MSI controller may feature a number of doorbells.
+
+- The payload (the value written to the doorbell).
+  
+  Devices may be configured to write an arbitrary payload chosen by software.
+  MSI controllers may have restrictions on permitted payloads.
+
+- Sideband information accompanying the write.
+  
+  Typically this is neither configurable nor probeable, and depends on the path
+  taken through the memory system (i.e. it is a property of the combination of
+  MSI controller and device rather than a property of either in isolation).
+
+
+MSI controllers:
+================
+
+An MSI controller signals interrupts to a CPU when a write is made to an MMIO
+address by some master. An MSI controller may feature a number of doorbells.
+
+Required properties:
+--------------------
+
+- msi-controller: Identifies the node as an MSI controller.
+
+Optional properties:
+--------------------
+
+- #msi-cells: The number of cells in an msi-specifier, required if not zero.
+
+  Typically this will encode information related to sideband data, and will
+  not encode doorbells or payloads as these can be configured dynamically.
+
+  The meaning of the msi-specifier is defined by the device tree binding of
+  the specific MSI controller. 
+
+
+MSI clients
+===========
+
+MSI clients are devices which generate MSIs. For each MSI they wish to
+generate, the doorbell and payload may be configured, though sideband
+information may not be configurable.
+
+Required properties:
+--------------------
+
+- msi-parent: A list of phandle + msi-specifier pairs, one for each MSI
+  controller which the device is capable of using.
+
+  This property is unordered, and MSIs may be allocated from any combination of
+  MSI controllers listed in the msi-parent property.
+
+  If a device has restrictions on the allocation of MSIs, these restrictions
+  must be described with additional properties.
+
+  When #msi-cells is non-zero, busses with an msi-parent will require
+  additional properties to describe the relationship between devices on the bus
+  and the set of MSIs they can potentially generate.
+
+
+Example
+=======
+
+/ {
+	#address-cells = <1>;
+	#size-cells = <1>;
+
+	msi_a: msi-controller at a {
+		reg = <0xa 0xf00>;
+		compatible = "vendor-a,some-controller";
+		msi-controller;
+		/* No sideband data, so #msi-cells omitted */
+	};
+
+	msi_b: msi-controller at b {
+		reg = <0xb 0xf00>;
+		compatible = "vendor-b,another-controller";
+		msi-controller;
+		/* Each device has some unique ID */
+		#msi-cells = <1>;
+	};
+
+	msi_c: msi-controller at c {
+		reg = <0xb 0xf00>;
+		compatible = "vendor-b,another-controller";
+		msi-controller;
+		/* Each device has some unique ID */
+		#msi-cells = <1>;
+	};
+
+	dev at 0 {
+		reg = <0x0 0xf00>;
+		compatible = "vendor-c,some-device";
+
+		/* Can only generate MSIs to msi_a */
+		msi-parent = <&msi_a>;
+	};
+
+	dev at 1 {
+		reg = <0x1 0xf00>;
+		compatible = "vendor-c,some-device";
+
+		/* 
+		 * Can generate MSIs to either A or B.
+		 */
+		msi-parent = <&msi_a>, <&msi_b 0x17>;
+	};
+
+	dev at 2 {
+		reg = <0x2 0xf00>;
+		compatible = "vendor-c,some-device";
+		/*
+		 * Has different IDs at each MSI controller.
+		 * Can generate MSIs to all of the MSI controllers.
+		 */
+		msi-parent = <&msi_a>, <&msi_b 0x17>, <&msi_c 0x53>;
+	};
+};
-- 
1.9.1