On Thu, Nov 01, 2012 at 01:00:43PM -0400, Alan Stern wrote: > On Thu, 1 Nov 2012, Greg KH wrote: > > > On Thu, Nov 01, 2012 at 08:59:11AM -0700, Sarah Sharp wrote: > > > On Mon, Oct 29, 2012 at 04:28:39PM +0800, Lan Tianyu wrote: > > > > This patch is to set xhci root hub's DeviceRemovable according to usb port's > > > > connect type which currently comes from ACPI information. If ACPI information > > > > was different with PORTSC, there would be a warning. > > > > > > You should also add the note here that you're trusting the ACPI tables > > > over the xHCI DeviceRemovable port status register bits when you decide > > > whether to mark a port as hard-wired. Tianyu is doing it this way > > > because Windows is likely to rely on the ACPI tables over the > > > DeviceRemovable bits. > > > > "Likely"? Is that going to be tested anywhere in the Windows test > > suites? > > > > I would think that the bits would be more reliable than the ACPI tables. > > I would expect that the ACPI tables and other parts of the BIOS are > easier for manufacturers to update than the settings in other system > components (like xHCI controllers). Even an end user can re-flash the > BIOS. > > Of course, that doesn't mean the ACPI values are always going to be > right; firmware-derived values are notoriously unreliable. And as for > which values Windows will rely upon, probably only the people in > Redmond know for sure. That was bad wording, sorry. I know that the Intel developers who designed this mechanism have advised Microsoft to use the APCI tables. In fact, they weren't even aware of the DeviceRemovable bits until I told them about it. Microsoft's own documentation talks about the ACPI tables as well, see: http://msdn.microsoft.com/en-us/library/windows/hardware/ff553550%28v=vs.85%29.aspx So, AFAIK, Microsoft will be using the ACPI tables to determine which ports are safe to power off. Sarah Sharp -- 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
