Hi Greg KH, On Tue, Apr 28, 2015 at 12:42:24PM +0200, Greg KH wrote: > On Sun, Apr 19, 2015 at 11:46:12AM +0800, Zhuang Jin Can wrote: > > Some usb3 devices may not support usb3 lpm well. > > The patch adds a sysfs to enable/disable u1 or u2 of the port.The > > settings apply to both before and after device enumeration. > > Supported values are "0" - u1 and u2 are disabled, "u1" - only u1 is > > enabled, "u2" - only u2 is enabled, "u1_u2" - u1 and u2 are enabled. > > > > The interface is useful for testing some USB3 devices during > > development, and provides a way to disable usb3 lpm if the issues can > > not be fixed in final products. > > How is a user supposed to "know" to make this setting for a device? Why > can't the kernel automatically set this value properly? Why does it > need to be a kernel issue at all? > By default kernel enables u1 u2 of all USB3 devices. This interface provides the user to change this policy. User may set the policy according to PID/VID of uevent or according to the platform information known by userspace. It's not a kernel issue, as u1 u2 is mandatory by USB3 compliance. But for some internal hardwired USB3 connection, e.g. SSIC, passing USB3 compliance is not mandatory. So the interface provides a way for vendor to ship with u1 or u2 broken products. Of course, this is not encouraged :). > And when you are doing development of broken devices, the kernel doesn't > have to support you, you can run with debugging patches of your own > until you fix your firmware :) > Understood. But I think other vendor or developer may face the same issue in final product shipment or during development. Moreover, the interface provide the flexibility for developer to separately disable/enable u1 or u2, e.g. If they're debugging an u2 issue, they can disable u1 to simplify the situtation. Thanks Jincan -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
