Date: Mon, 30 Jun 2014 10:52:20 +0100
From: Will Deacon <will.deacon@arm.com>
To: Olav Haugan <ohaugan@codeaurora.org>
Cc: Mark Rutland <Mark.Rutland@arm.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-samsung-soc@vger.kernel.org" 
	<linux-samsung-soc@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Pawel Moll <Pawel.Moll@arm.com>,
        Ian Campbell <ijc+devicetree@hellion.org.uk>,
        Grant Grundler <grundler@chromium.org>, Joerg Roedel <joro@8bytes.org>,
        Stephen Warren <swarren@wwwdotorg.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Marc Zyngier <Marc.Zyngier@arm.com>,
        Linux IOMMU <iommu@lists.linux-foundation.org>,
        Rob Herring <robh+dt@kernel.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        Kumar Gala <galak@codeaurora.org>,
        "linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
        Cho KyongHo <pullip.cho@samsung.com>,
        Dave P Martin <Dave.Martin@arm.com>,
        "linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
        Hiroshi Doyu <hdoyu@nvidia.com>
Subject: Re: [PATCH v2] devicetree: Add generic IOMMU device tree bindings
Message-ID: <20140630095220.GA25779@arm.com>
References: <1400877218-4113-1-git-send-email-thierry.reding@gmail.com>
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 <20140624091808.GC26013@arm.com>
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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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