On Mon, Mar 21, 2022 at 10:17:34AM -0500, Rob Herring wrote: > On Mon, Mar 21, 2022 at 5:49 AM Marc Zyngier <maz@xxxxxxxxxx> wrote: > > > > Since 6dce5aa59e0b ("PCI: xgene: Use inbound resources for setup") was > > merged in the 5.5 time frame, PCIe on the venerable XGene platform has > > been unusable: 6dce5aa59e0b broke both XGene-1 (Mustang and m400) and > > XGene-2 (Merlin), while the addition of c7a75d07827a ("PCI: xgene: Fix > > IB window setup") fixed XGene-2, but left the rest of the zoo > > unusable. > > > > It is understood that this systems come with "creative" DTs that don't > > match the expectations of modern kernels. However, there is little to > > be gained by forcing these changes on users -- the firmware is not > > upgradable, and the current owner of the IP will deny that these > > machines have ever existed. > > The gain for fixing this properly is not having drivers do their own > dma-ranges parsing. We've seen what happens when drivers do their own > parsing of standard properties (e.g. interrupt-map). Currently, we > don't have any drivers doing their own parsing: > > $ git grep of_pci_dma_range_parser_init > drivers/of/address.c:int of_pci_dma_range_parser_init(struct > of_pci_range_parser *parser, > drivers/of/address.c:EXPORT_SYMBOL_GPL(of_pci_dma_range_parser_init); > drivers/of/address.c:#define of_dma_range_parser_init > of_pci_dma_range_parser_init > drivers/of/unittest.c: if (of_pci_dma_range_parser_init(&parser, np)) { > drivers/pci/of.c: err = of_pci_dma_range_parser_init(&parser, dev_node); > include/linux/of_address.h:extern int > of_pci_dma_range_parser_init(struct of_pci_range_parser *parser, > include/linux/of_address.h:static inline int > of_pci_dma_range_parser_init(struct of_pci_range_parser *parser, > > And we can probably further refactor this to be private to drivers/pci/of.c. > > For XGene-2 the issue is simply that the driver depends on the order > of dma-ranges entries. > > For XGene-1, I'd still like to understand what the issue is. Reverting > the first fix and fixing 'dma-ranges' should have fixed it. I need a > dump of how the IB registers are initialized in both cases. Happy to provide that for the m400 if told how :) -dann > I'm not > saying changing 'dma-ranges' in the firmware is going to be required > here. There's a couple of other ways we could fix that without a > firmware change, but first I need to understand why it broke.