[+cc Marc] On Tue, Mar 06, 2018 at 11:57:03AM +0800, Icenowy Zheng wrote: > 在 2018-03-05一的 15:47 -0600，Bjorn Helgaas写道： > > On Mon, Mar 05, 2018 at 10:50:58PM +0800, Icenowy Zheng wrote: > > > Hi everyone, > > > > > > I'm trying to implement a driver for the quirky (DW) PCIe RC in the > > > Allwinner H6 SoC. > > > > > > The quirk is that only the "dbi" space is always mapped, but at the > > > same time only 64KiB of other spaces (config, downstream IO and > > > non- > > > prefetchable memory) are accessible. To access a certain address > > > the > > > high 16-bit of the address (all bus addresses in H6 SoC are 32-bit > > > despite the CPU is 64-bit) needs to be written into the > > > PCIE_ADDR_PAGE_CFG register (a vendor-defined register in DBI > > > space). > > > So the access to these spaces cannot be processed correctly with > > > just > > > readl/writel, as the existing code does. > > > > > > Is it possible to workaround this in the PCI subsystem of Linux? > > > > > > (I have thought a workaround that only maps the current accessible > > > 64KiB with the MMU, and when accessing the non-accessible part, > > > catch > > > the page fault and re-setup the map to the new 64KiB page. But > > > surely > > > it will kill the performance.) > > > > If you only need to write to PCIE_ADDR_PAGE_CFG for *config* > > accesses, > > this should be easy. All config accesses go through wrappers > > (pci_read_config_word(), etc) and several host bridge drivers have to > > update a register with parts of the config address, e.g., > > advk_pcie_rd_conf(), mvebu_pcie_hw_rd_conf(). > > > > It sounds like you also need to update PCIE_ADDR_PAGE_CFG for I/O > > port > > accesses. I/O port accesses do go through a wrapper (inb(), etc), so > > it might be possible in principle to intercept these, although much > > more difficult than config accesses, because the config accesses are > > already set up with per-host bridge hooks, while the I/O port > > accessors are mostly per-arch. > > > > But if you have to update PCIE_ADDR_PAGE_CFG for memory accesses, > > that's really a problem because drivers are allowed to essentially > > read a memory BAR, convert that bus address to a CPU physical memory > > address, ioremap() it, then directly access the PCIe memory with > > loads > > and stores. > > Unfortunately this is the case. All above (config, IO, memory) needs > PCIE_ADDR_PAGE_CFG update. tango_pcie_probe() has a similar issue. We don't have a good solution there, so we just live with the fact that the platform will be unreliable. Bjorn
