Stephen Warren <swarren@xxxxxxxxxxxxx> wrote @ Wed, 30 Oct 2013 23:33:32 +0100: > > + are required. This unique ID info can be used to calculate > > + MC_SMMU_<SWGROUP name>_ASID_0 offset and HOTRESET bit. > > I'm afraid I still don't quite understand what a swgroup is. > > IIUC, the HW works like this based on comments in a previous patch: > > Each bus-master attached to the MMU passes a "memory client ID" along > with the transaction. Some devices can generate transactions with > different "memory client IDs". There is a mapping inside the SMMU from > "memory client ID" to "address space ID". (I don't know what form that > mapping takes; can you point out where it's set up?). Each "address > space ID" has its own set of page tables. Right. "memory client ID" is used to find out MC_SMMU_<swgroup>_ASID_0 register. This register is used to associate <swgroup> to address space(AS). <swgroup> == H/W. <swgroup> can be attached to any AS. > Is "swgroup" simply another name for "memory client ID"? If so, it'd > be good to use just one term consistently. I used the name "memory client ID" because this ID can be used to find out HOTRESET bit in MC_CLIENT_HOTRESET_*_0 registers in addition to find the MC_SMMU_<swgroup>_ASID_0 offset. But maybe it's easy to use the consistent name as "swgroup". If laster HOTRESET wants automatic calculation they could borrow/redefine the same ID list, just replacing the prefix. What do you think? > Assuming "swgroup" is "memory client ID", Yes > why can't the driver just > create a list/... of known swgroups at runtime, based on the swgroup > values that each device uses, which would presumably be either > hard-coded in the client device's driver, or represented in the DT smmu > property's "iommu specifier" value. Why we have "nvidia,swgroups" is just to avoid a device node having a wrong "nvidia,memory-clients" which is not supported by that Tegra SoC, which could crash kernel eventually. This info may be residual since we define both "nvidia,swgroups" and "nvidia,memory-clients" at once in DT. I'll remove "nvidia,swgroups" in SMMU node. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
