On 11/11/2013 04:39 AM, Will Deacon wrote: > On Mon, Nov 11, 2013 at 08:31:53AM +0000, Hiroshi Doyu wrote: >> An "IOMMU device" on the bus is poplulated first, "IOMMU'able devices" >> are done later. >> >> With CONFIG_OF_IOMMU, "#stream-id-cells" DT binding would be used to >> identify whether a device is IOMMU'able or not. If a device is >> IOMMU'able, we'll defer to populate that device till an iommu device >> is populated. Once an iommu device is populated, "dev->bus->iommu_ops" >> is set in the bus. Then, those defered IOMMU'able devices are >> populated and configured as IOMMU'abled with help of the already >> populated iommu device via iommu_ops->add_device(). >> >> Signed-off-by: Hiroshi Doyu <[email protected]> >> --- >> Update: >> This is newly added, and the successor of the following RFC: >> [RFC][PATCHv3+ 1/2] driver/core: Add of_iommu_attach() >> http://lists.linuxfoundation.org/pipermail/iommu/2013-November/006914.html > > This generally looks like the right idea to me, but it would be good to have > the input from a DT maintainer on the use of "#stream-id-cells" as an > indicator > that a device is behind an IOMMU. (aside: I think "iommuable" is a horrible > word!). > > What happens if you do the deferring at the bus level? E.g. defer all device > probes on a bus, until the IOMMU is probed for that bus. That might fit > better with future work, where we will almost certainly need to expose more > of the bus topology to Linux. Of course, I can see that falling down for > monolithic virtual buses like the platform bus.
I don't think it's correct to think about "the IOMMU for the bus". There could easily be multiple different IOMMU slave-sides attached to a bus, and hence you'd need to defer probing until "all the IOMMs for the bus" to be available. Equally, I assume that dev->bus->iommu_ops rather assumes that bus masters always master transactions onto the same bus that their control registers are slaves upon. That also doesn't seem like a reasonable assumption. As such, I think an approach where each device waits for any IOMMUs that affect it (wherever/whatever and however many they may be) is better than one where we try to explicitly manage the probe order of devices based on their slave registers' location. -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
