From mboxrd@z Thu Jan 1 00:00:00 1970 From: ohaugan@codeaurora.org (Olav Haugan) Date: Tue, 24 Jun 2014 14:35:54 -0700 Subject: [PATCH v2] devicetree: Add generic IOMMU device tree bindings In-Reply-To: <20140624181150.GB4067@arm.com> References: <1400877218-4113-1-git-send-email-thierry.reding@gmail.com> <4545972.cM7IP1qTXQ@wuerfel> <53A4C0C9.2050908@codeaurora.org> <20140624091808.GC26013@arm.com> <53A9BC18.2090106@codeaurora.org> <20140624181150.GB4067@arm.com> Message-ID: <53A9EF3A.2070704@codeaurora.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 6/24/2014 11:11 AM, Will Deacon wrote: > 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 at 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. I am talking about SMMU_SMRn[MASK] register bits. This is not something that can be dynamically detected at run-time. It is configuration at the same level as the actual StreamIDs. Thanks, Olav Haugan -- The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation