On Wed, Aug 14, 2019 at 02:12:07PM -0600, Nick Crews wrote: > Thanks for the fast response! > > On Tue, Aug 13, 2019 at 12:02 AM Greg Kroah-Hartman > <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > On Mon, Aug 12, 2019 at 06:08:43PM -0600, Nick Crews wrote: > > > Hi Greg! > > > > Hi! > > > > First off, please fix your email client to not send html so that vger > > does not reject your messages :) > > Thanks, should be good now. > > > > > > I am working on a Chrome OS device that supports a policy called "USB Power > > > Share," which allows users to turn the laptop into a charge pack for their > > > phone. When the policy is enabled, power will be supplied to the USB ports > > > even when the system is in low power states such as S3 and S5. When > > > disabled, then no power will be supplied in S3 and S5. I wrote a driver > > > <https://lore.kernel.org/patchwork/patch/1062995/> for this already as part > > > of drivers/platform/chrome/, but Enric Balletbo i Serra, the maintainer, > > > had the reasonable suggestion of trying to move this into the USB subsystem. > > > > Correct suggestion. > > > > > Has anything like this been done before? Do you have any preliminary > > > thoughts on this before I start writing code? A few things that I haven't > > > figured out yet: > > > - How to make this feature only available on certain devices. Using device > > > tree? Kconfig? Making a separate driver just for this device that plugs > > > into the USB core? > > > - The feature is only supported on some USB ports, so we need a way of > > > filtering on a per-port basis. > > > > Look at the drivers/usb/typec/ code, I think that should do everything > > you need here as this is a typec standard functionality, right? > > Unfortunately this is for USB 2.0 ports, so it's not type-C. > Is the type-C code still worth looking at? If this is for USB 2, does it use the "non-standard" hub commands to turn on and off power? If so, why not just use the usbreset userspace program for that? And how are you turning a USB 2 port into a power source? That feels really odd given the spec. Is this part of the standard somewhere or just a firmware/hardware hack that you are adding to a device? Is there some port information in the firmware that describes this functionality? If so, can you expose it through sysfs to the port that way? thanks, greg k-h
