On Wed, Apr 29, 2015 at 06:57:30PM +0800, Zhuang Jin Can wrote: > On Wed, Apr 29, 2015 at 11:01:48AM +0200, Greg KH wrote: > > On Wed, Apr 29, 2015 at 03:20:04PM +0800, Zhuang Jin Can wrote: > > > On Tue, Apr 28, 2015 at 11:11:10PM +0200, Greg KH wrote: > > > > On Wed, Apr 29, 2015 at 12:51:27AM +0800, Zhuang Jin Can wrote: > > > > > 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. > > > > > > > > And why would they ever want to do that? > > > > > > > > > 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 :). > > > > > > > > If the state is broken for those devices, we can't require the user to > > > > fix it for us, the kernel should do it automatically. > > > > > > > > > > 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. > > > > > > > > For debugging only, perhaps, but for a "normal" user, please let's > > > > handle this automatically and don't create a switch that never gets used > > > > by anyone or anything. > > > > > > > Thanks Greg. Since so far the patch has no interesting value to the > > > community, I'll drop the patch. > > > > I didn't say that, I said it needed some more work to be accepted. > Sorry for misunderstanding. Let me explain more why we need this interface. > > We have a modem USB3 device (in stepping C) hardwired to one specific port of xHCI. > The device was expected to work with u1 u2, however, due to a HW issue, it doesn't > work stably. To workaround the issue, we let the init.rc script disable u1 u2 for > this specific port. Modern Linux systems don't have init.rc scripts anymore :) > Then maybe we want to start debug u1 issue first, to avoid hitting u2 issue, > we can disable u2. After u1 issue is resolved, we can enable back u2 to continue to > debug u2 issue. This provides the flexibility to isolate u1 u2 debugging. > This is valuable I think :) I agree. > The HW issue will be fixed in stepping D, however C and D will have the same PID/VID. > There's no way for kernel to know the difference between C and D. > Even after fixing in D, C will still be used for development (to save money..) That sounds like a big design flaw, what about looking at the version of the device? That's what that field in the USB descriptors is for. > If somehow finally we decide to ship stepping C (suppose HW issue can't be fixed in D in time), > we'll have to disable both u1 and u2. > > If we fix only u1 issue, we can just disable u2, etc.. > > To summarize, it provide users an opptunity to change the u1 u2 policy to > debug and ship broken products. That's good, but you need to do it somehow "automatically", as again, systems don't have a init.rc file anymore :) thanks, greg k-h -- 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
