What is difference between role switch procedures ?

[amit251291]

We were exploring role switch for imx8qm-Android9-Auto. 

I came to know that role switch can be possible by changing right role (host | gadget) in 

/sys/bus/platform/devices/ci_hdrc.0/role

During testing we could see that roles are getting changed and based on the roles it was enumerating Iphone. 

This is one case. But during my exploration i also found chipidea document which also explains role switching using HNP and SRP protocols. We tried this but it doesn't works after step 2. 

I wanted to understand the difference between the 2 procedures. Could you please throw some light here ??

[igorpadykov · Accepted solution]

Hi Amit

 there are two USB controllers:

- One is USB2 compatible and the IP comes from ChipIdea (the same USB IP used on mx5/mx6/mx7)

- One is USB3 compatible and the IP comes from Cadence.

The Cadence USB controller is described like this in arch/arm64/boot/dts/freescale/imx8-ss-conn.dtsi:

usbotg3: usb3@5b110000 {
compatible = "Cadence,usb3";

....

The Chipidea USB controller is described like this in arch/arm64/boot/dts/freescale/imx8-ss-conn.dtsi:

usbotg1: usb@5b0d0000 {
compatible = "fsl,imx8qm-usb", "fsl,imx7ulp-usb",
"fsl,imx27-usb";

....

Best regards
igor
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[amit251291]

Dear igor,

Thanks for  clarification. I have found answer with your explanation.