On 25/08/2017 17:45, Robin Murphy wrote: > On 25/08/17 16:35, Mason wrote: > >> On 25/08/2017 17:25, Robin Murphy wrote: >> >>> On 25/08/17 16:01, Mason wrote: >>> >>>> Robin wrote a prophetic post back in March: >>>> http://lists.infradead.org/pipermail/linux-arm-kernel/2017-March/492965.html >>>> >>>>> The appropriate DT property would be "dma-ranges", i.e. >>>>> >>>>> pci@... { >>>>> ... >>>>> dma-ranges = <(PCI bus address) (CPU phys address) (size)>; >>>>> } >>>> >>>> The dma-ranges property seems to be exactly what I'm looking for: >>>> >>>> Restrict DMA to the first X MB of RAM (use a bounce buffer >>>> for other physical addresses). >>>> >>>> I added the following property to my PCIe node >>>> >>>> dma-ranges = <0x0 0x80000000 0x80000000 0x20000000>; >>>> >>>> with the intent to create a 1:1 mapping for [0x80000000, 0xa0000000[ >>>> >>>> But it does not work. Arg! >>>> >>>> My PCIe controller driver seems to be correctly calling of_dma_get_range: >>>> >>>> [ 0.520469] [<c03d85e8>] (of_dma_get_range) from [<c03d5ad8>] (of_dma_configure+0x48/0x234) >>>> [ 0.520483] [<c03d5ad8>] (of_dma_configure) from [<c02fa154>] (pci_device_add+0xac/0x350) >>>> [ 0.520493] [<c02fa154>] (pci_device_add) from [<c02fa488>] (pci_scan_single_device+0x90/0xb0) >>>> [ 0.520501] [<c02fa488>] (pci_scan_single_device) from [<c02fa500>] (pci_scan_slot+0x58/0x100) >>>> [ 0.520510] [<c02fa500>] (pci_scan_slot) from [<c02fb418>] (pci_scan_child_bus+0x20/0xf8) >>>> [ 0.520519] [<c02fb418>] (pci_scan_child_bus) from [<c02fb6e8>] (pci_scan_root_bus_msi+0xcc/0xd8) >>>> [ 0.520527] [<c02fb6e8>] (pci_scan_root_bus_msi) from [<c02fb70c>] (pci_scan_root_bus+0x18/0x20) >>>> [ 0.520537] [<c02fb70c>] (pci_scan_root_bus) from [<c0310544>] (pci_host_common_probe+0xc8/0x314) >>>> [ 0.520546] [<c0310544>] (pci_host_common_probe) from [<c0310ce8>] (tango_pcie_probe+0x148/0x350) >>>> [ 0.520557] [<c0310ce8>] (tango_pcie_probe) from [<c034d398>] (platform_drv_probe+0x34/0x6c) >>>> >>>> of_dma_get_range() is called on the pcie node (which is expected) >>>> but after parsing n_addr_cells and n_size_cells in the while loop, >>>> the code jumps to the parent node ("soc")... while my property is >>>> attached to the pcie node... >>> >>> This is not your driver calling of_dma_get_range(), this is the PCI core >>> doing so in the act of DMA master configuration for a discovered >>> *endpoint*. The fact that the "pass the host controller's OF node >>> because we don't have one for the endpoint" bodge only works properly >>> for dma-coherent and not dma-ranges is a known, but irrelevant, problem. >>> >>> If your host controller driver needs to discover its windows from DT to >>> configure *itself*, it needs to parse dma-ranges itself; see pcie-iproc, >>> pcie-racar, pcie-xgene, etc. for examples. >> >> Yes, I'm aware that I need to do my own parsing of dma-ranges. >> I can use that information to configure BAR0.base and the >> region registers. >> >> But Linux needs to record my settings at some point, right? >> Otherwise, how does the DMA framework know that devices can >> only reach cpu addresses [0x80000000, 0xa0000000[ and when >> to use bounce buffers? >> >> What's preventing the XHCI driver from allocating memory >> outside of my "safe" range, and having the DMA framework >> blindly map that? > > At the moment, nothing. Systems that have physical memory that is not > visible in PCI mem space are having a bad time and will not go to space > today. > > But that bears no relation to your MSI controller getting its doorbell > address set appropriately. OK, so this is what I propose for v11 in order to not hard code the MSI doorbell address (e.g. 0xa002e07c) I add the following property to the pcie node: dma-ranges = <0x0 0x80000000 0x80000000 0x20000000>; I.e. pci_addr = 0x80000000, cpu_addr = 0x80000000, len=0x20000000 Then in the PCIe driver, I parse dma-ranges. Consequently MSI_doorbell_addr = cpu_addr + len + res.start + 0x7c Bjorn, Marc, Robin, is that an acceptable solution? Tangent: Robin, for my own education, how does one configure the DMA framework to use bounce buffers for certain addresses? Regards.
