Hi Oliver, On Tue, Jun 21, 2016 at 10:43:05PM +0200, Oliver Neukum wrote: > On Tue, 2016-06-21 at 16:58 +0300, Heikki Krogerus wrote: > > On Tue, Jun 21, 2016 at 03:08:52PM +0200, Oliver Neukum wrote: > > > > > The firmware will surely want to display something. So it is possible > > > that we start the OS will a valid power contract. How do we deal > > > with that? Renegotiate? > > > > Systems where the firmware has to negotiate PD will likely provide > > firmware interface like UCSI, and where the OS has no direct > > interaction with the USB PD transceiver. In these case there is no > > need to renegotiate as we are just reporting in OS the initial state > > after bootup. > > How certain is that? I was under the impression that on many systems > the OS would speak to the TCPM directly. I think we gonna see systems where the OS has access to TCPC and where the TCPM is expected to be implemented in the OS, but we will have quite a few systems where the TCPC/PD controller/non TCPC compliant Type-C PHY is attached to a microcontroller like EC, and where that microcontroller will implement TCPM and the OS is exposed just a separate interface, most likely UCSI. > > We do have a system where the typec port is used to power the board. > > On these systems the firmware does not communicate PD (so we will > > never have the firmware displaying anything over Type-C on those > > systems), but the USB PD chargers for example are detected as 3.0A > > Type-C power supplies before any USB PD negotiation takes place, just > > like the spec says, and that is more then enough to power these boards. > > Now correct me, if I am misreading the spec. I am sure the system > will boot unless it needs ridiculous amounts of power, but > will we see anything on the screen? As far as I can tell the spec > actually says that you cannot enter an alternate mode without having > established a power contract. > If we really leave entering modes up to user space, we have lost > printk before getting into the initrd at the earliest. With these boards, you will not see anything on the screen that is attached to a Type-C connector until the OS has booted to the point where it has negotiated the power contract and entered a mode. If the system has BIOS/FW/EC capable of negotiating the power contract and enter a mode, but where we still are expected to take over the whole TCPM in OS, I think the connection will be reset. Thanks, -- heikki -- 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
