I would like to add CDP (charging downstream port) capability over my OTG port in host mode. I am using an iMX6q platform with Chipidea HDRC (highspeed dual role controller) with 4.1 kernel. Looked at a bunch of documents like USB Battery Charging Specification and USB Power Delivery specification, it is clear that there is a handshake over D+ and D- before enumeration to identify whether a host supports CDP or not. It occurs in two steps. A primary handshake to detect SDP vs CDP/ DCP where host will respond with D- voltage greater than 0.3 V and less than 0.8 V. A secondary handshake to detect CDP vs DCP where DCP will be indicated witha response of D+ voltage greater than 0.3 V and less than 0.8 V. I believe the handshake can only be supported by using a CDP emulator or a USB charging port controller. But I would like to investigate the possibility of achieving this handshake with only driver changes in PHY or controller i.e. without any additional hardware chips or circuitry. Does anyone have any viewpoints on whether CDP charging can be achieved without any additional hardware changes over Chipidea HDRC in host mode? Thank you. -- 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
