On 30/06/2020 18:16, Krishna Reddy wrote: >> OK, well I see what you are saying, but if we intended to support all 3 for Tegra194, then we should ensure all 3 are initialised correctly. > > The driver intend to support up to 3 instances. It doesn't really mandate that all three instances be present in same DT node. > Each mmio aperture in "reg" property is an instance here. reg = <inst0_base, size>, <inst1_base, size>, <inst2_base, size>; > The reg can have all three or less and driver just configures based on reg and it works fine. So it sounds like we need at least 2 SMMUs (for non-iso and iso) but we have up to 3 (for Tegra194). So the question is do we have a use-case where we only use 2 and not 3? If not, then it still seems that we should require that all 3 are present. The other problem I see here is that currently the arm-smmu binding defines the 'reg' with a 'maxItems' of 1, whereas we have 3. I believe that this will get caught by the 'dt_binding_check' when we try to populate the binding. >> It would be better to query the number of SMMUs populated in device-tree and then ensure that all are initialised correctly. > > Getting the IORESOURCE_MEM is the way to count the instances driver need to support. > In a way, It is already querying through IORESOURCE_MEM here. Yes I was wondering that. I think we just need to decide if the 3rd SMMU is optional or not. The DT binding should detail and min and max supported. Jon -- nvpublic
