On Sun, Dec 15, 2013 at 04:18:23AM +0800, Bjorn Helgaas wrote: > [+cc devicetree, linux-arm-kernel] > > On Sat, Dec 14, 2013 at 1:05 PM, shiv prakash Agarwal > <chhotu.shiv@xxxxxxxxx> wrote: > > On Sun, Dec 15, 2013 at 12:29 AM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote: > >> On Sat, Dec 14, 2013 at 11:32 AM, shiv prakash Agarwal > >> <chhotu.shiv@xxxxxxxxx> wrote: > >>> Hi All, > >>> > >>> How devices config spaces are mapped to host memory? > >>> Is it being handled by core driver? I could not locate. > >> > >> The PCI core does not map config space into memory. That's not even > >> possible for the legacy config access methods, e.g., using I/O ports > >> 0xcf8 and 0xcfc [1]. > >> > >> If you're wondering about how Linux uses ECAM, that's mostly in > >> arch/x86/pci/mmconfig*. That code does ioremap the ECAM area into > >> kernel virtual space, but only for access via pci_read_config_word(), > >> pci_write_config_word(), etc. > >> > >> Bjorn > >> > >> [1] http://en.wikipedia.org/wiki/PCI_configuration_space#Software_implementation > > > > Thanks Bjorn for quick reply, > > > > Above reference says: > > During system initialization, firmware determines the base address for > > this “stolen” address region and communicates it to the root complex > > and to the operating system. This communication method is > > implementation-specific, and not defined in the PCI Express > > specification. > > > > How above is implemented on ARM? > > On x86, we learn the ECAM address via ACPI (the MCFG table or a host > bridge _CBA method). I don't know how this is done on ARM. I could > imagine it being done via device tree, but I really don't know. > Unfortunately both the address discovery and the actual ECAM accesses > are in arch-specific code. Yes, it comes from device tree. DT sends CPU address range allocated for cfg transfers. pci_read_config_word and pci_write_config_word send bdf and offset. Address translation unit of your RC driver should be programmed in such a way that it translates cpu address to the cfg address based on bdf and offset. You can see one such implementation in drivers/pci/host/pcie-designware.c Regards Pratyush > > Bjorn > -- > To unsubscribe from this list: send the line "unsubscribe linux-pci" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
