On Tuesday, July 12, 2016 6:57:10 AM CEST Bharat Kumar Gogada wrote: > Hi, > > I have a query. > > Can any once explain the purpose of pci_remap_iospace function in root port driver. > > What is its dependency with architecture ? > > Here is my understanding, the above API takes PCIe IO resource and its to be mapped CPU address from > ranges property and remaps into virtual address space. > > So my question is who uses this virtual addresses ? The inb()/outb() functions declared in asm/io.h > When End Point requests for IO BARs doesn't it get > from the above resource range (first parameter of API) and > do ioremap to access this region ? Device drivers generally do not ioremap() the I/O BARs but they use inb()/outb() directly. They can also call pci_iomap() and do ioread8()/iowrite8() on the pointer returned from that function, but generally the call to pci_iomap() then returns a pointer into the virtual address that is already mapped. > But why root complex driver is mapping this address region ? The PCI core does not know that the I/O space is memory mapped. On x86 and a few others, I/O space is not memory mapped but requires the use of special CPU instructions. Arnd -- 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
