On 10/06/16 13:44, Sergei Shtylyov wrote:

On 6/10/2016 1:19 PM, Roger Quadros wrote:

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It provides APIs for the following tasks

- Registering an OTG/dual-role capable controller
- Registering Host and Gadget controllers to OTG core
- Providing inputs to and kicking the OTG state machine

Provide a dual-role device (DRD) state machine.
DRD mode is a reduced functionality OTG mode. In this mode
we don't support SRP, HNP and dynamic role-swap.

In DRD operation, the controller mode (Host or Peripheral)
is decided based on the ID pin status. Once a cable plug (Type-A
or Type-B) is attached the controller selects the state
and doesn't change till the cable in unplugged and a different
cable type is inserted.

As we don't need most of the complex OTG states and OTG timers
we implement a lean DRD state machine in usb-otg.c.
The DRD state machine is only interested in 2 hardware inputs
'id' and 'b_sess_vld'.

Signed-off-by: Roger Quadros <redacted>

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[...]

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+/**
+ * usb_otg_register_gadget - Register the gadget controller to OTG core
+ * @gadget:    gadget controller

   We call that USB device controller (UDC). I'm not sure what you meant here...
   And what about the 2nd arg, 'ops'?

There are 2 data structures representing the Device controller.

struct usb_gadget - represents a usb slave device
struct usb_udc -struct usb_udc - describes one usb device controller

usb_udc is for private use only. usb_otg_register_gadget() takes struct usb_gadget
as argument.

Do you want me to refer to struct usb_gadget as UDC?

   No.

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What is wrong with calling it gadget controller?

   It's not a controller, it's a piece of software AFAIU. Or is my English just too weak? :-)

Everything at this point is a piece of software :).

struct usb_gadget, represents the gadget controller device not the driver (or software).

struct usb_gadget_driver represents the gadget function driver.
struct usb_gadget_ops represents the UDC driver ops.