Hello, Adding Greg & Hans just in case they have an idea, or someone else to ping in mind. Miquel Raynal <miquel.raynal@xxxxxxxxxxx> wrote on Wed, 3 Apr 2019 10:13:43 +0200: > Hello, > > I am reading the document named "xHCI interoperability testing v0.94" > available on usb.org. There is this paragraph: > > Devices operating at Enhanced SuperSpeed GenX are allowed to > draw a maximum configured current of 900mA and unconfigured > current of 150mA. Devices operating at High-Speed or below may > draw a maximum configured current of 500mA and unconfigured > current of 100mA*. Devices must report their maximum configured > current draw and their power configuration as self or bus > powered to the host and must operate within the regions > reported. Additionally any device that is in the suspended > state may draw no more than 2.5 mA. > > My understanding is that the current limitation on Vbus should be tuned > dynamically between 100, 150, 500 and 900mA depending on the type of > device and if has been configured or not. > > Despite some researches in the USB core I can't find any mechanism > handling this in Linux implementation. > > Behind this remark, I actually have boards (Armada 7040/8040 DB) with a > regulator on Vbus to limit the current to either 500 or 900mA. I > checked the xhci-platform driver which is used with these SoCs and I > don't find any mean to tweak this value depending on the inserted > device. > > Should I actually care? Is it enough to limit to 900mA whenever the > xHCI driver is probed? > > Thanks for your guidance, > Miquèl Thanks, Miquèl
