On Wed, 2016-06-22 at 12:31 +0300, Heikki Krogerus wrote: Hi, > > 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. Think about a DP over type C display with a USB PD power brick on a daisy chain. If the host needs more than 15W or more than 5V, a reset is suicide. And losing earlyprintk hurts a lot. This means we need USB PD statically in the kernel. And a kernel based policy that brings up all displays. Regards Oliver -- 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
