On Wed, Jan 03, 2024 at 11:33:35AM +0530, Kishon Vijay Abraham I wrote: > Hi Niklas, Hello Kishon! > > > I assume dw_pcie_ep_map_addr(), writel(), dw_pcie_ep_unmap_addr() have > > > to happen atomically so nobody else uses that piece of the ATU while > > > we're doing this? There's no mutex here, so I guess we must know this > > > is atomic already because of something else? > > > > Most devices have multiple iATUs (so multiple iATU indexes). > > > > pcie-designware-ep.c:dw_pcie_ep_outbound_atu() > > uses find_first_zero_bit() to make sure that a specific iATU (index) > > is not reused for something else: > > https://github.com/torvalds/linux/blob/v6.7-rc7/drivers/pci/controller/dwc/pcie-designware-ep.c#L208 > > > > A specific iATU (index) is then freed by dw_pcie_ep_unmap_addr(), > > which does a clear_bit() for that iATU (index). > > > > It is a bit scary that there is no mutex or anything, since > > find_first_zero_bit() is _not_ atomic, so if we have concurrent calls > > to dw_pcie_ep_map_addr(), things might break, but that is a separate > > issue. > > There cannot be concurrent calls to dw_pcie_ep_map_addr() in the current > code path as pci_epc_raise_irq(), pci_epc_map_addr() and > pci_epc_unmap_addr() which invokes dw_pcie_ep_map_addr() takes EPC lock in > pci-epc-core. I must have overlooked the mutex in pci-epc-core. Thank you for clearing that up. Kind regards, Niklas
