On Mon, Apr 22, 2024 at 01:25:21PM +0530, Manivannan Sadhasivam wrote: > > > > What I would like is more consistency between the EPF drivers. > > > > I guess an if-statement that skips the pci_epc_map_addr() in pci-epf-test > > if using eDMA would make pci-epf-mhi and pci-epf-test most consistent. > > > > Agree. > > 1) Do we want to rely on the fact that hopefully none of the iATUs in the DWC > > controller has configured a mapping that might mess things up for us? > > I don't see why the PCI/DMA address of the remote buffer, supplied to > > pci-epf-test via test_reg BAR, might not fall within the physical iATU window > > on the local EP system. (As long as the PCI EPF driver has mapped any address > > using pci_epc_map_addr().) > > > > This is a big argument that EPF drivers running on a DWC-based EPC should > > definitely NOT call pci_epc_map_addr() needlessly when using eDMA, as it > > can be catastrophic. (pci-epf-test needs to be patched.) > > > > Right. There is no need to do iATU translation for DMA. I avoid that in MHI > driver. There is no need for pci_epc_map_addr() when using DMA_SLAVE *for DWC-based controllers*. Are we certain that this will not break pci-epf-test for non DWC-based controllers? > > 2) Can we really assume that both pci-epf-test and pci-epf-mhi does not need > > to call pci_epc_map_addr() when using a DMA_SLAVE DMA controller? > > This seems to be designed only with DWC in mind. Other PCIe endpoint > > controllers might require this. > > (Yes, for DWC-based controllers, this definitely should be skipped, but EPF > > drivers are supposed to be independent from a specific EPC.) > > > > For TEST yes, but for MHI, no. In MHI, I kind of mix both iATU and DMA to ripe > most of the performance (small vs big transactions). But for the TEST driver, it > is fair to not call pci_epc_map_addr() when DMA_SLAVE is supported. I agree that we should definitely skip pci_epc_map_addr() in pci-epf-test when using DMA_SLAVE on DWC-based controllers, but I don't feel comfortable in submitting a patch that does this unconditionally for pci-epf-test.c, as I don't know how the DMA hardware in: drivers/pci/controller/cadence/pcie-cadence-ep.c drivers/pci/controller/pcie-rcar-ep.c drivers/pci/controller/pcie-rockchip-ep.c works, and I do not want to regress them. I did suggest that DWC-based drivers could set a DMA_SLAVE_SKIP_MEM_MAP flag or similar when registering the eDMA, which pci-epf-test then could check, but I got no response if anoyone else thought that this was a good idea. Kind regards, Niklas
