On Thu, Oct 25, 2012 at 9:36 AM, Sarah Sharp <sarah.a.sharp@xxxxxxxxxxxxxxx> wrote: > On Thu, Oct 25, 2012 at 12:31:09PM +0530, shashank chaturvedi wrote: >> Hi sarah, >> I am using Ubuntu 11.04 OS and NEC USB3.0 Host controller. >> I want to write the PLS [8:5] field in the PORTSC register through C >> program ,as per xhci spec first we have to write the LWS field >> I am doing that also, But its unable to write above fields. >> Can you help me for how to write these field of PORTSC register? >> I am sending you the code below. Please provide me the solution for >> writing the PLS field of PORTSC register > > Why would you want to do that? For link power management? What is the > xHCI kernel driver not providing you such that you have to write a > userspace program? > > If you're trying to write the PLS register from userspace while the xHCI > driver is loaded, I don't think that will work. The PCI registers have > already been mapped by the xHCI driver, and I don't think another > program would be able to map them again. > > But I'm not sure, since I've never attempted to memory map PCI registers > from userspace. I was under the impression that you just can't do that. PORTSC looks like an xHCI-specific register that would be inside one of the BARs (xHCI spec sec 5.4.8). This would typically be mapped by the driver. Writing it from userspace behind the driver's back is asking for trouble because the driver owns the device, and it won't be aware of what you're doing. PCI config space isn't mapped by drivers in the same way PCI BARs are, and you can change things there with "setpci". But again, this is asking for trouble because those registers are really owned by the PCI core, and things will go wrong if you change things behind its back. Bjorn -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
