01.10.2020 14:04, Nicolin Chen пишет: > On Thu, Oct 01, 2020 at 12:23:16PM +0200, Thierry Reding wrote: > > > >>>>>> It looks to me like the only reason why you need this new global API is >>>>>>>>>> because PCI devices may not have a device tree node with a phandle to >>>>>>>>>> the IOMMU. However, SMMU support for PCI will only be enabled if the >>>>>>>>>> root complex has an iommus property, right? In that case, can't we >>>>>>>>>> simply do something like this: >>>>>>>>>> >>>>>>>>>> if (dev_is_pci(dev)) >>>>>>>>>> np = find_host_bridge(dev)->of_node; >>>>>>>>>> else >>>>>>>>>> np = dev->of_node; > >>> I personally am not a fan of adding a path for PCI device either, >>> since PCI/IOMMU cores could have taken care of it while the same >>> path can't be used for other buses. >> >> There's already plenty of other drivers that do something similar to >> this. Take a look at the arm-smmu driver, for example, which seems to be >> doing exactly the same thing to finding the right device tree node to >> look at (see dev_get_dev_node() in drivers/iommu/arm-smmu/arm-smmu.c). > > Hmm..okay..that is quite convincing then... Not very convincing to me. I don't see a "plenty of other drivers", there is only one arm-smmu driver. The dev_get_dev_node() is under CONFIG_ARM_SMMU_LEGACY_DT_BINDINGS (!). Guys, doesn't it look strange to you? :) The arm-smmu driver does a similar thing for the modern bindings to what Nicolin's v3 is doing. >>> If we can't come to an agreement on globalizing mc pointer, would >>> it be possible to pass tegra_mc_driver through tegra_smmu_probe() >>> so we can continue to use driver_find_device_by_fwnode() as v1? >>> >>> v1: https://lkml.org/lkml/2020/9/26/68 >> >> tegra_smmu_probe() already takes a struct tegra_mc *. Did you mean >> tegra_smmu_probe_device()? I don't think we can do that because it isn't > > I was saying to have a global parent_driver pointer: similar to > my v1, yet rather than "extern" the tegra_mc_driver, we pass it > through egra_smmu_probe() and store it in a static global value > so as to call tegra_smmu_get_by_fwnode() in ->probe_device(). > > Though I agree that creating a global device pointer (mc) might > be controversial, yet having a global parent_driver pointer may > not be against the rule, considering that it is common in iommu > drivers to call driver_find_device_by_fwnode in probe_device(). You don't need the global pointer if you have SMMU OF node. You could also get driver pointer from mc->dev->driver. But I don't think you need to do this at all. The probe_device() could be invoked only for the tegra_smmu_ops and then seems you could use dev_iommu_priv_set() in tegra_smmu_of_xlate(), like sun50i-iommu driver does.
