linux-kernel - Re: [PATCH 1/3] Docs: dt: add generic MSI bindings

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Date:	Fri, 24 Jul 2015 08:04:22 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	David Daney <ddaney@...iumnetworks.com>
Cc:	Mark Rutland <Mark.Rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Will Deacon <Will.Deacon@....com>,
	Robin Murphy <Robin.Murphy@....com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	"arnd@...db.de" <arnd@...db.de>,
	"treding@...dia.com" <treding@...dia.com>,
	"majun258@...wei.com" <majun258@...wei.com>,
	"thunder.leizhen@...wei.com" <thunder.leizhen@...wei.com>,
	"tirumalesh.chalamarla@...iumnetworks.com" 
	<tirumalesh.chalamarla@...iumnetworks.com>,
	"laurent.pinchart@...asonboard.com" 
	<laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH 1/3] Docs: dt: add generic MSI bindings

On Thu, 23 Jul 2015 19:26:11 +0100
David Daney <ddaney@...iumnetworks.com> wrote:

> On 07/23/2015 09:52 AM, Mark Rutland wrote:
> [...]
> > +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.
> > +
> 
> We say here that "msi-parent" consists of pairs ...
> 
> > +  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@a {
> > +		reg = <0xa 0xf00>;
> > +		compatible = "vendor-a,some-controller";
> > +		msi-controller;
> > +		/* No sideband data, so #msi-cells omitted */
> > +	};
> > +
> > +	msi_b: msi-controller@b {
> > +		reg = <0xb 0xf00>;
> > +		compatible = "vendor-b,another-controller";
> > +		msi-controller;
> > +		/* Each device has some unique ID */
> > +		#msi-cells = <1>;
> > +	};
> > +
> > +	msi_c: msi-controller@c {
> > +		reg = <0xb 0xf00>;
> > +		compatible = "vendor-b,another-controller";
> > +		msi-controller;
> > +		/* Each device has some unique ID */
> > +		#msi-cells = <1>;
> > +	};
> > +
> > +	dev@0 {
> > +		reg = <0x0 0xf00>;
> > +		compatible = "vendor-c,some-device";
> > +
> > +		/* Can only generate MSIs to msi_a */
> > +		msi-parent = <&msi_a>;
> 
> 
> My device-tree syntax foo is a little rusty, but doesn't "msi-parent" 
> need a pair of elements?  This has only the phandle.

This is a pair in the sense of (phandle, msi-specifier).

msi_a doesn't have a #msi-cells, so its msi-specifier is of size 0. In
that case, the pair is (phandle, empty-set).

You could also have something like:

	msi_d: msi-controller@d {
		#msi-cells = <2>;
	};

	dev@f {
		msi-parent = <&msi_d 0x1 0x2>;
	};

and msi-parent in this case would still be a pair, with an
msi-specifier of size 2.

Hope this helps,

	M.
-- 
Without deviation from the norm, progress is not possible.
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