Varun Sethi <Varun.Sethi@xxxxxxxxxxxxx> writes: > Hi Hiroshi, > >> -----Original Message----- >> From: Hiroshi Doyu [mailto:hdoyu@xxxxxxxxxx] >> Sent: Thursday, August 14, 2014 9:35 PM >> To: Sethi Varun-B16395 >> Cc: Hiroshi Doyu; Thierry Reding; Stephen Warren; Arnd Bergmann; Will >> Deacon; Mark Rutland; devicetree@xxxxxxxxxxxxxxx; Olof Johansson; >> iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; Rob Herring; linux-tegra@xxxxxxxxxxxxxxx; >> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx >> Subject: Re: [PATCH v5] devicetree: Add generic IOMMU device tree bindings >> >> Hi Varun, >> >> Varun Sethi <Varun.Sethi@xxxxxxxxxxxxx> writes: >> >> >> -----Original Message----- >> >> From: iommu-bounces@xxxxxxxxxxxxxxxxxxxxxxxxxx [mailto:iommu- >> >> bounces@xxxxxxxxxxxxxxxxxxxxxxxxxx] On Behalf Of Hiroshi Doyu >> >> Sent: Thursday, August 14, 2014 12:18 PM >> >> To: Thierry Reding; Stephen Warren; Arnd Bergmann; Will Deacon >> >> Cc: Mark Rutland; devicetree@xxxxxxxxxxxxxxx; Olof Johansson; >> >> iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; Rob Herring; >> >> linux-tegra@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx >> >> Subject: Re: [PATCH v5] devicetree: Add generic IOMMU device tree >> >> bindings >> >> >> >> >> >> Thierry Reding <thierry.reding@xxxxxxxxx> writes: >> >> >> >> > +Multiple-master IOMMU: >> >> > +---------------------- >> >> > + >> >> > + iommu { >> >> > + /* the specifier represents the ID of the master */ >> >> > + #iommu-cells = <1>; >> >> > + }; >> >> > + >> >> > + master@1 { >> >> > + /* device has master ID 42 in the IOMMU */ >> >> > + iommus = <&{/iommu} 42>; >> >> > + }; >> >> > + >> >> > + master@2 { >> >> > + /* device has master IDs 23 and 24 in the IOMMU */ >> >> > + iommus = <&{/iommu} 23>, <&{/iommu} 24>; >> >> > + }; >> >> >> >> I think that this "master ID" will be parsed in IOMMU driver. For >> >> example, ARM,SMMU expects "streamID" as "master ID", right? >> >> >> >> If a SoC has a feature to configure to assign streamID to devices at >> >> runtime, "streamID" is not equal to "master ID". >> >> >> >> iommus = <&{/smmu} "soc specific master ID">; >> >> >> >> "soc master ID" needs to be translated into "streamID" by SoC SW. It >> >> seems that ARM,SMMU kernel driver doesn't expect this kind of ID >> >> translation. If ARM,SMMU kernel driver is used as is, "soc master ID" >> >> would be incompatible? ARM,SMMU needs such translation before >> >> parsing. Is this my understanding right? >> >> >> >> If so I think that this master ID configuration/translation may be >> >> quite reasonable requirment for SoC using ARM,SMMU. >> >> >> >> Can we consider this ID translation within ARM,SMMU compatibility? >> >> >> >> IOW, is it possible to implement some SoC specific hook for ID >> >> translation/configuration in ARM,SMMU kernel driver? >> > >> > >> > Can the id translation be done using a SMR mask? >> >> No, "SoC master ID" is completely independenf of SMR. >> >> > Also, for dynamic stream ID allocation we would need to represent the >> > specific master register (to store the stream ID) in the device tree. >> >> I assmue that the above means that iMX has such configuration register to map >> steramID and a device dynamically. > > We have per master registers for setting the stream ID on the > Layerscape platforms. My point was that we would need the iommu master > node to include a reference to the master id register. > > master@1 { > /* device has master ID 42 in the IOMMU */ > iommus = <&{/iommu} 42>; > master-id-reg = <phandle offset> > }; In the above, for "iommus=" bindings, you wouldn't need to break ARM,SMMU compatibility at all if you set "streamID" exactly as below. master@1 { /* device has master ID 42 in the IOMMU */ iommus = <&{/iommu} 'any given streamID'>; master-id-reg = <phandle offset> }; And your SoC needs to register bus_notifier and ADD_DEVICE should configure to map 'any given streamID' to a device via the above register. This wouldn't need any modification from ARM,SMMU driver and keep the iommus bindings as it is. IOW, SoC only needs to register ADD_DEVICE in bus_notifier to map StreamID to a device. This needs to be executed earlier than IOMMU bus's ADD_DEVICE, though. Is my understanding right? -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
