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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <5c2e12ff-5a48-1f2a-2f72-77d257f97c1b@microchip.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/17/21 7:28 AM, Cristian.Birsan@microchip.com wrote: > Hi Heikki, > > On 2/16/21 11:12 AM, Heikki Krogerus wrote: >> >> Hi Cristian, >> >> On Mon, Feb 15, 2021 at 05:25:29PM +0000, Cristian.Birsan@microchip.com wrote: >>> My name is Cristian and I'm working on bringing up a USB Type-C Port Controller >>> (TCPC) without Power Delivery support which is intended to work with USB 2.0 >>> Host/Device. >>> >>> The IP is integrated into one of Microchip's SoCs, it is memory-mapped and it >>> was designed based on USB Type-C Cable and Connector specification revision 1.2. >>> >>> In brief, it has support for detecting the threshold voltages on CC1, CC2 lines, >>> control of the current source (Ip), and pull-down resistors (Rd). The management >>> of the controller is to be implemented in software (it is not autonomous). >>> >>> Having in mind that the controller uses proprietary registers, I chose to >>> implement it using TCPM directly and skip the TCPC Interface. >>> >>> For the beginning, I would like to enable simple use cases like the ones >>> described in Connection State Diagram: Source and Connection State Diagram: Sink >>> from USB Type-C Cable and Connector Specification. >>> >>> Some of the problems that I encountered until now are: >>> >>> 1. tcpm_register_port() fails if set_pd_rx(), pd_transmit() or set_vconn() >>> functions are missing. >>> >>> 2. the port capabilities are specified in the connector DT bindings only through >>> PDOs, even though PDOs are specific to PD mode. >>> >>> 3. once I was able to start the TCPM state machine, it called pd_transmit() in >>> the process to negotiate the capabilities. For my case I used a dummy function >>> just to be able to register the port. >>> >>> Please let me know what you think and if you have any advice. Am I going in the >>> right direction or is there a better way to implement this? >> >> Don't bother with tcpm if you don't have PD support. Just register >> your port(s) and the partners directly with the connector class: >> https://www.kernel.org/doc/html/latest/driver-api/usb/typec.html >> >> You can use the driver for the TI HD3SS3220 controller as an example >> how to do that (drivers/usb/typec/hd3ss3220.c). That thing is also >> just USB Type-C PHY without PD support just like your port controller. >> > > Thank you for the suggestion. I had a look at the driver you mentioned and also > other drivers from the same folder. The chips have logic embedded into > them to handle CC lines and VBUS while the controller on which I'm working > provides basic access to CC lines and it is up to the software to drive it. > VBUS is to be detected/enabled through a standard GPIO. > > The reason for which I tried to use TCPM is that I need to implement in software > the Sink/Source Connection State Diagrams, CC debounce, and VBUS management. > I tried to avoid code duplication but on the other hand, my use case does not > involve PD. > > If there are better chances to upstream the driver using just the connector > class, I'll move forward with this direction. I just wanted to make sure I > explained correctly may use case before implementing it. > Personally I think it would be a bad idea to make the mandatory functions optional. PD is an integral part of tcpm, after all. How about implementing dummy functions as needed ? Thanks, Guenter