linux-kernel - RE: [PATCH 2/3] Docs: dt: Add PCI MSI map bindings

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Date:	Wed, 5 Aug 2015 19:53:59 +0000
From:	Stuart Yoder <stuart.yoder@...escale.com>
To:	Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
CC:	"lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
	"arnd@...db.de" <arnd@...db.de>,
	"marc.zyngier@....com" <marc.zyngier@....com>,
	"will.deacon@....com" <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ddaney@...iumnetworks.com" <ddaney@...iumnetworks.com>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"tirumalesh.chalamarla@...iumnetworks.com" 
	<tirumalesh.chalamarla@...iumnetworks.com>,
	"laurent.pinchart@...asonboard.com" 
	<laurent.pinchart@...asonboard.com>,
	"thunder.leizhen@...wei.com" <thunder.leizhen@...wei.com>,
	"treding@...dia.com" <treding@...dia.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"majun258@...wei.com" <majun258@...wei.com>
Subject: RE: [PATCH 2/3] Docs: dt: Add PCI MSI map bindings

> From: Mark Rutland <mark.rutland@....com>
> Date: Thu, Jul 23, 2015 at 11:52 AM

[cut]

> diff --git a/Documentation/devicetree/bindings/pci/pci-msi.txt
> b/Documentation/devicetree/bindings/pci/pci-msi.txt
> new file mode 100644
> index 0000000..9b3cc81
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/pci/pci-msi.txt
> @@ -0,0 +1,220 @@
> +This document describes the generic device tree binding for describing the
> +relationship between PCI devices and MSI controllers.
> +
> +Each PCI device under a root complex is uniquely identified by its Requester ID
> +(AKA RID). A Requester ID is a triplet of a Bus number, Device number, and
> +Function number.
> +
> +For the purpose of this document, when treated as a numeric value, a RID is
> +formatted such that:
> +
> +* Bits [15:8] are the Bus number.
> +* Bits [7:3] are the Device number.
> +* Bits [2:0] are the Function number.
> +* Any other bits required for padding must be zero.
> +
> +MSIs may be distinguished in part through the use of sideband data accompanying
> +writes. In the case of PCI devices, this sideband data may be derived from the
> +Requester ID. A mechanism is required to associate a device with both the MSI
> +controllers it can address, and the sideband data that will be associated with
> +its writes to those controllers.
> +
> +For generic MSI bindings, see
> +Documentation/devicetree/bindings/interrupt-controller/msi.txt.
> +
> +
> +PCI root complex
> +================
> +
> +Optional properties
> +-------------------
> +
> +- msi-map: Maps a Requester ID to an MSI controller and associated
> +  msi-specifier data. The property is an arbitrary number of tuples of
> +  (rid-base,msi-controller,msi-base,length), where:
> +
> +  * rid-base is a single cell describing the first RID matched by the entry.
> +
> +  * msi-controller is a single phandle to an MSI controller
> +
> +  * msi-base is an msi-specifier describing the msi-specifier produced for the
> +    first RID matched by the entry.
> +
> +  * length is a single cell describing how many consecutive RIDs are matched
> +    following the rid-base.
> +
> +  Any RID r in the interval [rid-base, rid-base + length) is associated with
> +  the listed msi-controller, with the msi-specifier (r - rid-base + msi-base).
> +
> +- msi-map-mask: A mask to be applied to each Requester ID prior to being mapped
> +  to an msi-specifier per the msi-map property.

Can we extend the msi-map-mask definition to say:  "A mask value of 0x0 is valid
and indicates that no RIDs are _currently_ mapped to any msi-specifier."

We have an SoC with a programmable hardware table in the PCI controller that maps
requester ID to stream ID, so the overall msi-map (and iommu-map) definition fit
into that scheme.  But, we would like to be able make the RID->stream-ID mapping
decision _lazily_, in Linux, based on actual usage of PCI devices.

      pcie@...0000 {
              compatible = "fsl,ls2085a-pcie", "snps,dw-pcie";
              device_type = "pci";
              ...
              msi-map = <0x0 &msi_a 0x7 4>,
              msi-map-mask = <0x0>
      };

That specifies the there are 4 stream IDs starting at stream ID 0x7, 
but the requester ID's are not mapped (because the mask is 0x0).
This tells the PCI controller driver that there are 4 msi-specifiers
(e.g. stream IDs) available and what they are.

(same definition would apply to the iommu-map-mask)

Thanks,
Stuart