linux-kernel - Re: [PATCH v2] devicetree: Add generic IOMMU device tree bindings

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Message-ID: <20140630095220.GA25779@arm.com>
Date:	Mon, 30 Jun 2014 10:52:20 +0100
From:	Will Deacon <will.deacon@....com>
To:	Olav Haugan <ohaugan@...eaurora.org>
Cc:	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>, Arnd Bergmann <arnd@...db.de>,
	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>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Linux IOMMU <iommu@...ts.linux-foundation.org>,
	Rob Herring <robh+dt@...nel.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>,
	Dave P Martin <Dave.Martin@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Hiroshi Doyu <hdoyu@...dia.com>
Subject: Re: [PATCH v2] devicetree: Add generic IOMMU device tree bindings

Hi Olav,

On Fri, Jun 27, 2014 at 11:23:27PM +0100, Olav Haugan wrote:
> On 6/25/2014 2:18 AM, Will Deacon wrote:
> > Why can't it be dynamically detected? Whilst the StreamIDs are fixed in
> > hardware (from the SMMU architecture perspective), the SMRs are completely
> > programmable. Why doesn't something like Andreas's proposal work for you?
> > The idea there was to find the constant bits among the StreamIDs for a
> > master and create the mask accordingly.
> > 
> Lets say I have an IOMMU with 2 masters and 2 SMRn slots with the
> following stream IDs coming from the masters:
> 
> Master 1: 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28
> Master 2: 0x30
> 
> To make this work I would program SMR[0] with StreamID 0x20 and mask 0xF
> to ignore lower 4 bits. SMR[1] would just be StreamID 0x30 with mask 0x0.
> 
> However, I could also have an IOMMU with 2 masters and 9 SMRn slots with
> the following stream IDs:
> 
> Master 1: 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28
> Master 2: 0x29
> 
> Here I would program all SMRn and leave the mask to be 0 for all SMRn's.
> So how do I detect when to apply a mask or not?

You would aim to use the smallest number of SMRs per master possible.
You could probably use:

  Master 1: SMR[0].id == 0x20, SMR[0].mask = 0x07
            SMR[1].id == 0x28, SMR[1].mask = 0x00

  Master 2: SMR[2].id == 0x29, SMR[2].mask = 0x00

> I am not familiar with Andreas's proposal. Do you have a link?

  http://marc.info/?l=linux-arm-kernel&m=139110598005846&w=2

Note that since Calxeda went under, Andreas is unfortunately no longer
working on this.

Will
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