Re: [RFC][PATCH 0/9] USB: OTG Core functionality

[Roger Quadros]

On 18/03/15 19:37, Tony Lindgren wrote:
> * Roger Quadros <rogerq@xxxxxx> [150318 07:00]:
>> Hi,
>>
>> [NOTE: RFC only. Not for merge yet.]
>>
>> This is an attempt to centralize OTG functionality in the kernel.
>> Still work in progress but I wanted to get an early feedback
>> to avoid major rework. :) 
>>
>> 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 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 *parent_dev,
>>                                  struct otg_fsm_ops *fsm_ops);
>> int usb_otg_unregister(struct device *parent_dev);
>>
>> - Registering Host controllers to OTG core (used by hcd-core)
>> int usb_otg_register_hcd(struct usb_hcd *hcd);
>> 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);
>> 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);
>>
>> '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.
> 
> Sounds good to me. I take you're also planning to provide some
> common /sys/kernel/debug/otg type interfaces for OTG validation
> tests? For things like SRP etc.

Yes that's the plan.

cheers,
-roger

> 
> Regards,
> 
> Tony
>  
>> Usage model:
>> -----------
>>
>> - The OTG controller device is assumed to be the parent of
>> the host and gadget controller. It must call usb_otg_register()
>> before populating the host and gadget devices so that the OTG
>> core is aware that it is an OTG device before the host & gadget
>> register. The OTG controller must provide struct otg_fsm_ops *
>> which will be called by the OTG core depending on 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.
>>
>> - 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.
>> 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() since it is
>> the only external component that has the 'struct otg_fsm' handle.
>>
>> Pending items:
>> - We probably need a otg class.
>> - sysfs interface for application OTG inputs and OTG status information
>> - resolve symbol dependency for module use.
>> - otg driver for dwc3 core to get dual-role working on dra7-evm.
>>
>> cheers,
>> -roger
>>
>> Roger Quadros (9):
>>   usb: hcd: Introduce usb_start/stop_hcd()
>>   usb: gadget: add usb_gadget_start/stop()
>>   usb: otg: add OTG core
>>   usb: otg: hub: Notify OTG fsm when A device sets b_hnp_enable
>>   usb: hcd: adapt to OTG
>>   usb: gadget: udc: adapt to OTG
>>   usb: dwc3: adapt to OTG core
>>   usb: otg-fsm: Remove unused members in struct otg_fsm
>>   usb: otg-fsm: Add documentation for struct otg_fsm
>>
>>  drivers/usb/Makefile              |   1 +
>>  drivers/usb/common/Makefile       |   1 +
>>  drivers/usb/common/usb-otg.c      | 732 ++++++++++++++++++++++++++++++++++++++
>>  drivers/usb/common/usb-otg.h      |  71 ++++
>>  drivers/usb/core/Kconfig          |   8 +
>>  drivers/usb/core/hcd.c            | 153 +++++---
>>  drivers/usb/core/hub.c            |  11 +-
>>  drivers/usb/dwc3/core.c           | 101 ++++++
>>  drivers/usb/dwc3/core.h           |   6 +
>>  drivers/usb/dwc3/platform_data.h  |   1 +
>>  drivers/usb/gadget/udc/udc-core.c | 172 ++++++++-
>>  include/linux/usb/gadget.h        |   3 +
>>  include/linux/usb/hcd.h           |   2 +
>>  include/linux/usb/otg-fsm.h       |  81 ++++-
>>  include/linux/usb/usb-otg.h       |  86 +++++
>>  15 files changed, 1357 insertions(+), 72 deletions(-)
>>  create mode 100644 drivers/usb/common/usb-otg.c
>>  create mode 100644 drivers/usb/common/usb-otg.h
>>  create mode 100644 include/linux/usb/usb-otg.h
>>
>> -- 
>> 2.1.0
>>
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