Date: Tue, 24 Jun 2014 19:11:50 +0100
From: Will Deacon <will.deacon@arm.com>
To: Olav Haugan <ohaugan@codeaurora.org>
Cc: Arnd Bergmann <arnd@arndb.de>, Rob Herring <robherring2@gmail.com>,
        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>,
        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: <20140624181150.GB4067@arm.com>
References: <1400877218-4113-1-git-send-email-thierry.reding@gmail.com>
 <CAL_JsqKumG1PSFoVfeGpLLG+MjXFeF4aUjun=vv1BJpaxk0Byg@mail.gmail.com>
 <4545972.cM7IP1qTXQ@wuerfel>
 <53A4C0C9.2050908@codeaurora.org>
 <20140624091808.GC26013@arm.com>
 <53A9BC18.2090106@codeaurora.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <53A9BC18.2090106@codeaurora.org>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org

On Tue, Jun 24, 2014 at 06:57:44PM +0100, Olav Haugan wrote:
> On 6/24/2014 2:18 AM, Will Deacon wrote:
> > On Sat, Jun 21, 2014 at 12:16:25AM +0100, Olav Haugan wrote:
> >> We have multiple-master SMMUs and each master emits a variable number of
> >> StreamIDs. However, we have to apply a mask (the ARM SMMU spec allows
> >> for this) to the StreamIDs due to limited number of StreamID 2 Context
> >> Bank entries in the SMMU. If my understanding is correct we would
> >> represent this in the DT like this:
> >>
> >> 	iommu {
> >> 		#address-cells = <2>;
> >> 		#size-cells = <0>;
> >> 	};
> >>
> >> 	master@a {
> >> 		...
> >> 		iommus = <&iommu StreamID0 MASK0>,
> >> 			 <&iommu StreamID1 MASK1>,
> >> 			 <&iommu StreamID2 MASK2>;
> >> 	};
> > 
> > Stupid question, but why not simply describe the masked IDs? What use does
> > the `raw' ID have to Linux?
> 
> We do describe the masked StreamID (SID) but we need to specify the mask
> that the SMMU should apply to the incoming SIDs, right?
> 
> We have a bus master that emits 43 unique SIDs. However, we have only 40
> SMMU_SMRn registers in the SMMU. So we need to mask out some of the
> incoming SID bits so that the 43 SIDs can match one of 40 entries in the
> SMR.

Hmm, so you're talking about stream matching, right? That doesn't belong in
the device-tree. I appreciate that the current driver does a terrible job at
allocating the SMRs (it's bloody difficult!), but we should try to improve
the dynamic behaviour instead of moving configuration of the SMMU out into
device-tree, where it's inflexible at best.

There have been patches previously posted by Andreas Herrmann helping here.
I'd be glad to see them revived.

Will
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/