[PATCH v4 00/13] USB: OTG/DRD Core functionality

[Roger Quadros]

Hi,

This series centralizes OTG/Dual-role functionality in the kernel.
As of now I've got Dual-role functionality working pretty reliably on
dra7-evm and am437x-gp-evm.

DWC3 controller and platform related patches will be sent separately.

Series is based on Greg's usb-next tree.

Changelog:
---------
v4:
- Added DT support for tying otg-controller to host and gadget
 controllers. For DT we no longer have the constraint that
 OTG controller needs to be parent of host and gadget. They can be
 tied together using the "otg-controller" property.
- Relax the requirement for DT case that otg controller must register before
 host/gadget. We maintain a wait list of host/gadget devices
 waiting on the otg controller.
- Use a single struct usb_otg for otg data.
- Don't override host/gadget start/stop APIs. Let the controller
 drivers do what they want as they know best. Helper API is provided
 for controller start/stop that controller driver can use.
- Introduce struct usb_otg_config to pass the otg capabilities,
 otg ops and otg timer timeouts during otg controller registration.
- rebased on Greg's usb.git/usb-next

v3:
- all otg related definations now in otg.h
- single kernel config USB_OTG to enable OTG core and FSM.
- resolved symbol dependency issues.
- use dev_vdbg instead of VDBG() in usb-otg-fsm.c
- rebased on v4.2-rc1

v2:
- Use add/remove_hcd() instead of start/stop_hcd() to enable/disable
 the host controller
- added dual-role-device (DRD) state machine which is a much simpler
 mode of operation when compared to OTG. Here we don't support fancy
 OTG features like HNP, SRP, on the fly role-swap. The mode of operation
 is determined based on ID pin (cable type) and the role doesn't change
 till the cable type changes.

Why?:
----

Most of the OTG drivers have been dealing with the OTG state machine
themselves and there is a scope for code re-use. This has been
partly addressed by the usb/common/usb-otg-fsm.c but it still
leaves the instantiation of the state machine and OTG timers
to the controller drivers. We re-use usb-otg-fsm.c but
go one step further by instantiating the state machine and timers
thus making it easier for drivers to implement OTG functionality.

Newer OTG cores support standard host interface (e.g. xHCI) so
host and gadget functionality are no longer closely knit like older
cores. There needs to be a way to co-ordinate the operation of the
host and gadget in OTG mode. i.e. to stop and start them from a
central location. This central location should be the USB OTG core.

Host and gadget controllers might be sharing resources and can't
be always running. One has to be stopped for the other to run.
This can't be done as of now and can be done from the OTG core.

What?:
-----

The OTG core instantiates the OTG/DRD Finite State Machine
per OTG controller and manages starting/stopping the
host and gadget controllers based on the bus state.
    
It provides APIs for the following
    
- Registering an OTG capable controller
struct otg_fsm *usb_otg_register(struct device *dev,
                                 struct usb_otg_config *config);

int usb_otg_unregister(struct device *dev);

- Registering Host controllers to OTG core (used by hcd-core)
int usb_otg_register_hcd(struct usb_hcd *hcd, unsigned int irqnum,
                         unsigned long irqflags, struct otg_hcd_ops *ops);
int usb_otg_unregister_hcd(struct usb_hcd *hcd);


- Registering Gadget controllers to OTG core (used by udc-core)
int usb_otg_register_gadget(struct usb_gadget *gadget,
                            struct otg_gadget_ops *ops);
int usb_otg_unregister_gadget(struct usb_gadget *gadget);


- Providing inputs to and kicking the OTG state machine
void usb_otg_sync_inputs(struct otg_fsm *fsm);
int usb_otg_kick_fsm(struct device *hcd_gcd_device);

- Getting controller device structure from OTG state machine instance
struct device *usb_otg_fsm_to_dev(struct otg_fsm *fsm);

'struct otg_fsm' is the interface to the OTG state machine.
It contains inputs to the fsm, status of the fsm and operations
for the OTG controller driver.

- Helper APIs for starting/stopping host/gadget controllers
int usb_otg_start_host(struct otg_fsm *fsm, int on);
int usb_otg_start_gadget(struct otg_fsm *fsm, int on);

Usage model:
-----------

- The OTG core needs to know what host and gadget controllers are
linked to the OTG controller. For DT boots we can provide that
information by adding "otg-controller" property to the host and
gadget controller nodes that points to the right otg controller.
For legacy boot we assume that OTG controller is the parent
of the host and gadget controllers. For DT if "otg-controller"
property is not present then parent child relationship constraint
applies.

- The OTG controller driver must call usb_otg_register() to register
itself with the OTG core. It must also provide the required
OTG configuration, fsm operations and timer timeouts (optional)
via struct usb_otg_config. The fsm operations will be called
depending on the OTG bus state.

- The host/gadget core stacks are modified to inform the OTG core
whenever a new host/gadget device is added. The OTG core then
checks if the host/gadget is part of the OTG controller and if yes
then prevents the host/gadget from starting till both host and
gadget are registered, OTG state machine is running and the
USB bus state is appropriate to start host/gadget.
For this, APIs have been added to host/gadget stacks to start/stop
the controllers from the OTG core.
For DT boots, If the OTG controller hasn't yet been registered
while the host/gadget are added, the OTG core will hold it in a wait list
and register them when the OTG controller registers.

- No modification is needed for the host/gadget controller drivers.
They must ensure that their start/stop methods can be called repeatedly
and any shared resources between host & gadget are properly managed.
The OTG core ensures that both are not started simultaneously.

- The OTG core instantiates one OTG state machine per OTG controller
and the necessary OTG timers to manage OTG state timeouts.
If none of the otg features are set during usb_otg_register() then it
instanciates a DRD (dual-role device) state machine instead.
The state machine is started when both host & gadget register and
stopped when either of them unregisters. The controllers are started
and stopped depending on bus state.

- During the lifetime of the OTG state machine, inputs can be
provided to it by modifying the appropriate members of 'struct otg_fsm'
and calling usb_otg_sync_inputs(). This is typically done by the
OTG controller driver that called usb_otg_register().

--
cheers,
-roger

Roger Quadros (13):
  usb: otg-fsm: Add documentation for struct otg_fsm
  usb: otg-fsm: support multiple instances
  usb: otg-fsm: Prevent build warning "VDBG" redefined
  otg-fsm: move usb_bus_start_enum into otg-fsm->ops
  usb: hcd.h: Add OTG to HCD interface
  usb: gadget.h: Add OTG to gadget interface
  usb: otg: add OTG core
  usb: doc: dt-binding: Add otg-controller property
  usb: chipidea: move from CONFIG_USB_OTG_FSM to CONFIG_USB_OTG
  usb: hcd: Adapt to OTG core
  usb: core: hub: Notify OTG fsm when A device sets b_hnp_enable
  usb: gadget: udc: adapt to OTG core
  usb: otg: Add dual-role device (DRD) support

 Documentation/devicetree/bindings/usb/generic.txt |    5 +
 Documentation/usb/chipidea.txt                    |    2 +-
 MAINTAINERS                                       |    4 +-
 drivers/usb/Kconfig                               |    2 +-
 drivers/usb/Makefile                              |    1 +
 drivers/usb/chipidea/Makefile                     |    2 +-
 drivers/usb/chipidea/ci.h                         |    2 +-
 drivers/usb/chipidea/otg_fsm.c                    |    1 +
 drivers/usb/chipidea/otg_fsm.h                    |    2 +-
 drivers/usb/common/Makefile                       |    3 +-
 drivers/usb/common/usb-otg-fsm.c                  |   26 +-
 drivers/usb/common/usb-otg.c                      | 1223 +++++++++++++++++++++
 drivers/usb/common/usb-otg.h                      |   71 ++
 drivers/usb/core/Kconfig                          |   11 +-
 drivers/usb/core/hcd.c                            |   55 +-
 drivers/usb/core/hub.c                            |   10 +-
 drivers/usb/gadget/udc/udc-core.c                 |  124 ++-
 drivers/usb/phy/Kconfig                           |    2 +-
 drivers/usb/phy/phy-fsl-usb.c                     |    3 +
 include/linux/usb/gadget.h                        |   14 +
 include/linux/usb/hcd.h                           |   14 +
 include/linux/usb/otg-fsm.h                       |  116 +-
 include/linux/usb/otg.h                           |  191 +++-
 23 files changed, 1808 insertions(+), 76 deletions(-)
 create mode 100644 drivers/usb/common/usb-otg.c
 create mode 100644 drivers/usb/common/usb-otg.h

-- 
2.1.4

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