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

[Peter Chen <peter.chen@freescale.com>]

On Mon, Aug 24, 2015 at 04:21:11PM +0300, Roger Quadros wrote:
> 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

Roger, thanks for your hard work. Since it is complicated, and can't
know its correctness and scalable well just reading code. I will run
it for chipidea driver, wait some time please.

Peter
> 
> 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
> 

-- 

Best Regards,
Peter Chen