linux-kernel - Re: [PATCH] devicetree: Add generic IOMMU device tree bindings

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Date:	Tue, 20 May 2014 22:40:50 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Dave Martin <Dave.Martin@....com>
Cc:	Will Deacon <will.deacon@....com>,
	Mark Rutland <Mark.Rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Pawel Moll <Pawel.Moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Grant Grundler <grundler@...omium.org>,
	Joerg Roedel <joro@...tes.org>,
	Stephen Warren <swarren@...dotorg.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Marc Zyngier <Marc.Zyngier@....com>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Kumar Gala <galak@...eaurora.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Cho KyongHo <pullip.cho@...sung.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] devicetree: Add generic IOMMU device tree bindings

On Tuesday 20 May 2014 17:39:12 Dave Martin wrote:
> On Tue, May 20, 2014 at 04:26:59PM +0100, Will Deacon wrote:
> > On Tue, May 20, 2014 at 02:23:47PM +0100, Arnd Bergmann wrote:
> > > 	Bit#   33222222 22221111 11111100 00000000
> > > 	       10987654 32109876 54321098 76543210
> > > phys.hi cell:  npt000ss bbbbbbbb dddddfff rrrrrrrr
> > > phys.mid cell: hhhhhhhh hhhhhhhh hhhhhhhh hhhhhhhh
> > > phys.lo cell:  llllllll llllllll llllllll llllllll
> > > 
> > > where:
> > > n is 0 if the address is relocatable, 1 otherwise
> > > p is 1 if the addressable region is "prefetchable", 0 otherwise
> > > t is 1 if the address is aliased (for non-relocatable I/O),
> > >  below 1 MB (for Memory), or below 64 KB (for relocatable I/O).
> > > ss is the space code, denoting the address space
> > > bbbbbbbb is the 8-bit Bus Number
> > > ddddd is the 5-bit Device Number
> > > fff is the 3-bit Function Number
> > > rrrrrrrr is the 8-bit Register Number
> > > hh...hh is a 32-bit unsigned number
> > > ll...ll is a 32-bit unsigned number
> > > 
> > > We can ignore n, p, t and r here, and use the same format for a DMA
> > > address, then define an empty "dma-ranges" property. That would
> > > imply that using b/d/f is sufficient to identify each master at the
> > > iommu. Any device outside of the PCI host but connected to the same
> > > iommu can use the same notation to list the logical b/d/f that gets
> > > sent to the IOMMU in bus master transactions.
> > > 
> > > Do you think this is sufficient for the ARM SMMU, or do we need
> > > something beyond that?
> > 
> > I think it can define the common-cases for the existing implementations,
> > yes. I anticipate Stream-IDs becoming > 16-bit in the near future though,
> > so we'd need extra bits if we're describing other devices coming into the
> > SMMU.
> > 
> > Note that we already have a binding for the current SMMU driver, so I'm not
> > really in a position to shift over to a new binding until the next version of
> > the SMMU architecture comes along...
> 
> How much code relies on the meaning of the nptsbdf bits?

Not much at all, I think this was defined mostly for open firmware
client interfaces, which we don't use with FDT.

n, t and r are probably only used in PCI functions that are listed
in DT, not in the host bridge.

b/d/f I think is mostly used for the interrupt-maps property, when
describing hardwired interrupts.

p and s are used when setting up the translation for inbound MMIO
and PIO.

	Arnd
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