Re: [RFC][PATCH v2 00/13] USB: OTG/DRD Core functionality
From: Peter Chen
Date: Sun Apr 19 2015 - 23:08:29 EST
On Tue, Apr 14, 2015 at 01:41:47PM +0300, Roger Quadros wrote:
> This is an attempt to centralize OTG/Dual-role functionality in the kernel.
> As of now I've got Dual-role functionality working pretty reliably on
> dra7-evm. xhci side of things for OTG/DRD use are fixed in
> http://thread.gmane.org/gmane.linux.kernel/1923161
Hi Roger,
Currently, there are two main problems for DRD/OTG framework.
- For multi-platform supports, we may define CONFIG_USB_OTG, but the
gadget should not add its otg descriptor to its configuration
descriptors if it does not support one of otg features (SRP/HNP/ADP).
Macpaul Lin's patch set [1] is the right way to do it.
- We are lack of framework to handle OTG (DRD) switch, it is great you
are designing it. The main problem for this framework is how to handle
DRD/OTG FSM unify. My thought is we add two paths for them separate.
For easy, I suggest if the platform supports one of otg features, then
it goes to fully otg fsm, else it goes to simply otg fsm (like your drd
fsm). If you agree with it too, you may not need to add another "dr_mode"
value.
Peter
[1] http://www.spinics.net/lists/linux-usb/msg123927.html
>
> Changelog:
> ---------
> 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 *parent_dev,
> struct otg_fsm_ops *fsm_ops,
> bool drd_only);
> 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.
>
> 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.
>
> --
> 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
> usb: gadget: add usb_gadget_start/stop()
> usb: otg: add OTG core
> usb: hcd: Add hcd add/remove functions for OTG use
> usb: otg: Add dual-role device (DRD) support
> usb: otg: hub: Notify OTG fsm when A device sets b_hnp_enable
> usb: gadget: udc: adapt to OTG
> udc-core: fix lock circular dependency on udc_lock
> usb: add "dual-role" mode to dr_mode device tree helper
> usb: dwc3: add dual-role support
> ARM: dts: dra7x-evm: Enable dual-role for usb1
>
> Documentation/devicetree/bindings/usb/generic.txt | 2 +-
> arch/arm/boot/dts/dra7-evm.dts | 2 +-
> arch/arm/boot/dts/dra72-evm.dts | 2 +-
> drivers/usb/Makefile | 1 +
> drivers/usb/common/Makefile | 1 +
> drivers/usb/common/common.c | 1 +
> drivers/usb/common/usb-otg-fsm.c | 19 +-
> drivers/usb/common/usb-otg.c | 902 ++++++++++++++++++++++
> drivers/usb/common/usb-otg.h | 71 ++
> drivers/usb/core/Kconfig | 8 +
> drivers/usb/core/hcd.c | 24 +-
> drivers/usb/core/hub.c | 11 +-
> drivers/usb/dwc3/core.c | 146 +++-
> drivers/usb/dwc3/core.h | 6 +
> drivers/usb/dwc3/platform_data.h | 1 +
> drivers/usb/gadget/udc/udc-core.c | 119 ++-
> include/linux/usb/gadget.h | 3 +
> include/linux/usb/hcd.h | 3 +
> include/linux/usb/otg-fsm.h | 104 ++-
> include/linux/usb/otg.h | 1 +
> include/linux/usb/usb-otg.h | 95 +++
> 21 files changed, 1476 insertions(+), 46 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
>
--
Best Regards,
Peter Chen
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