Hi Thierry, Thierry Reding <thierry.reding@xxxxxxxxx> wrote @ Tue, 19 Nov 2013 11:25:07 +0100: > From earlier discussions I thought the goal was to actually defer this > until all nodes referred to by the iommus property were actually > registered. The above only checks that the phandles can be resolved to > valid struct device_node:s. That doesn't mean that an actual IOMMU has > been registered for it, only that the devices have been created. Currently "bus->iommu_ops" is set at the end of tegra_smmu_probe(). So if "bus->iommu_ops" is set, it means that an iommu instance is populated at that time. > If you really only rely on dev->bus->iommu_ops to be present, then there > is no need to go through the loop in the first place, since you have > access to it immediately through the struct device that's passed into > the function. As mentioned in the above, "bus->iommu_ops" is set when an iommu instance is populated. "iommus=" is used only to defer a device probe until an iommu instance shows up although multiple IOMMUs are not supported yet correctly as you pointed out. > Furthermore, relying on dev->bus->iommu_ops will prevent multiple IOMMUs > from being used at all, since only one IOMMU can register iommu_ops with > the bus, right? So I think what we really need here is a way to resolve > the IOMMU using a phandle and return the associated struct > iommu_ops. Multiple IOMMU support doesn't work right now. It needs to be discussed a bit more. > I also have some trouble understanding how the current IOMMU framework > is supposed to work together with multiple IOMMUs for one device. The > .add_device() callback seems to be missing crucial information to help > decide whether the device to be added is actually one that it covers. > Also with an of_iommu_attach() function, doesn't that become more or > less redundant? I understand what you meant. In the current tegra SMMU implementation, iommu_ops is set when an iommu is populated so that we cannot use iommu_ops before that time. That's why of_iommu_attach() was introduced here. I couldn't set iommu_ops at drvier init yet because we support SMMU and GART with a single image and the current IOMMU framework assume that there's one IOMMU on the bus. If we set iommu_ops at driver init, the latter one would overwrite it. -- 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
