Re: [PATCH v3 00/11] USB: OTG/DRD Core functionality
On 16/07/15 21:29, Andrew Bresticker wrote:
Hi Roger,
On Wed, Jul 15, 2015 at 6:26 AM, Roger Quadros rog...@ti.com wrote:
Hi Andrew,
On 13/07/15 22:14, Andrew Bresticker wrote:
Hi Roger,
On Wed, Jul 8, 2015 at 3:19 AM, Roger Quadros rog...@ti.com wrote:
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.
I'm wondering if the requirement that the OTG controller be the parent
of the USB host/device-controllers makes sense. For some context, I'm
working on adding dual-role support for Tegra210, specifically on a
system with USB Type-C. On Tegra, the USB host-controller and USB
device-controller are two separate IP blocks (XUSB host and XUSB
device) with another, separate, IP block (XUSB padctl) for the USB PHY
and OTG support. In the non-Type-C case, your OTG framework could
work well, though it's debatable as to whether or not the XUSB padctl
device should be a parent to the XUSB host/device-controller devices
(currently it isn't - it's just a PHY provider). But in the Type-C
case, it's an off-chip embedded controller that determines the
dual-role status of the Type-C port, so the above requirement doesn't
make sense at all.
My idea was to have the OTG/DRD controller explicitly specify its host
and device controllers, so in DT, something like:
otg-controller {
...
device-controller = usb_device;
host-controller = usb_host;
...
};
usb_device: usb-device@ {
...
};
usb_host: usb-host@... {
...
};
What do you think?
I agree that we need to support your use case but how to do it
is not yet clear to me.
In your above example the otg controller knows what are the host
and gadget controllers but the host/gadget devices don't
know who is their otg controller.
So the problem is that when usb_otg_register_hcd/gadget() is called
we need to get a handle to the otg controller.
One solution I see is to iterate over the registered otg_controller_list
and check if we match the host/gadget controller in there.
Then there is also a possibility that host/gadget controllers get
registered before the OTG controller. Then we can't know for sure if
the host/gadget controller was meant for dual-role operation or not
and it will resort to single role operation.
Any idea to prevent the above situation?
Maybe we need to add some logic in host/gadget cores to check if the port
is meant for dual-role use and defer probe if OTG controller is not yet
registered?
In the DT case, I think we could add an otg-controller property to
the host and gadget nodes, and in usb_otg_register_{hcd,gadget}()
check for that property and defer probe if the referenced OTG
controller has not yet been registered. Not sure how to indicate that
a host/gadget is meant for dual-role operation on non-DT platforms
though.
Sounds fine for DT case.
For non DT case I don't see any other way to connect the OTG controller
to the host/gadget controllers other than the parent child relationship.
Maybe for non DT case we can still have that constraint.
We can have this constraint regardless so that DT users who fit
in that model don't need to add 'otg-controller' property.
cheers,
-roger
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Re: [PATCH v3 00/11] USB: OTG/DRD Core functionality
Hi Roger,
On Wed, Jul 15, 2015 at 6:26 AM, Roger Quadros rog...@ti.com wrote:
Hi Andrew,
On 13/07/15 22:14, Andrew Bresticker wrote:
Hi Roger,
On Wed, Jul 8, 2015 at 3:19 AM, Roger Quadros rog...@ti.com wrote:
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.
I'm wondering if the requirement that the OTG controller be the parent
of the USB host/device-controllers makes sense. For some context, I'm
working on adding dual-role support for Tegra210, specifically on a
system with USB Type-C. On Tegra, the USB host-controller and USB
device-controller are two separate IP blocks (XUSB host and XUSB
device) with another, separate, IP block (XUSB padctl) for the USB PHY
and OTG support. In the non-Type-C case, your OTG framework could
work well, though it's debatable as to whether or not the XUSB padctl
device should be a parent to the XUSB host/device-controller devices
(currently it isn't - it's just a PHY provider). But in the Type-C
case, it's an off-chip embedded controller that determines the
dual-role status of the Type-C port, so the above requirement doesn't
make sense at all.
My idea was to have the OTG/DRD controller explicitly specify its host
and device controllers, so in DT, something like:
otg-controller {
...
device-controller = usb_device;
host-controller = usb_host;
...
};
usb_device: usb-device@ {
...
};
usb_host: usb-host@... {
...
};
What do you think?
I agree that we need to support your use case but how to do it
is not yet clear to me.
In your above example the otg controller knows what are the host
and gadget controllers but the host/gadget devices don't
know who is their otg controller.
So the problem is that when usb_otg_register_hcd/gadget() is called
we need to get a handle to the otg controller.
One solution I see is to iterate over the registered otg_controller_list
and check if we match the host/gadget controller in there.
Then there is also a possibility that host/gadget controllers get
registered before the OTG controller. Then we can't know for sure if
the host/gadget controller was meant for dual-role operation or not
and it will resort to single role operation.
Any idea to prevent the above situation?
Maybe we need to add some logic in host/gadget cores to check if the port
is meant for dual-role use and defer probe if OTG controller is not yet
registered?
In the DT case, I think we could add an otg-controller property to
the host and gadget nodes, and in usb_otg_register_{hcd,gadget}()
check for that property and defer probe if the referenced OTG
controller has not yet been registered. Not sure how to indicate that
a host/gadget is meant for dual-role operation on non-DT platforms
though.
Thanks,
Andrew
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Re: [PATCH v3 00/11] USB: OTG/DRD Core functionality
On 13/07/15 16:04, Li Jun wrote: On Mon, Jul 13, 2015 at 01:24:05PM +0300, Roger Quadros wrote: Hi, On 10/07/15 10:58, Li Jun wrote: On Wed, Jul 08, 2015 at 01:19:26PM +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. xhci side of things for OTG/DRD use are already in v4.2 Do you have any plan to implement OTG(HNP) on some of your platforms based on this OTG core? Not yet but Joao Pinto was interested to implement full OTG for dwc3 controllers. Would you be interested to try out one of your platforms so that we can address any issues early? cheers, -roger Yes, I am considering to try out OTG on chipidea driver for FSL i.mx6x platform , which will based on your OTG core and my previous gadget update patchset. Great :) I will comment your patchset if find any issues. Since there is still much work to do to complete OTG HNP/SRP, so I assume this will not be done in a short time. Yes. My plan was to first get DRD working reliably and then add missing HNP/SRP stuff. The first user of HNP/SRP will know what issues are and what needs to be added. cheers, -roger -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH v3 00/11] USB: OTG/DRD Core functionality
Hi Andrew,
On 13/07/15 22:14, Andrew Bresticker wrote:
Hi Roger,
On Wed, Jul 8, 2015 at 3:19 AM, Roger Quadros rog...@ti.com wrote:
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.
I'm wondering if the requirement that the OTG controller be the parent
of the USB host/device-controllers makes sense. For some context, I'm
working on adding dual-role support for Tegra210, specifically on a
system with USB Type-C. On Tegra, the USB host-controller and USB
device-controller are two separate IP blocks (XUSB host and XUSB
device) with another, separate, IP block (XUSB padctl) for the USB PHY
and OTG support. In the non-Type-C case, your OTG framework could
work well, though it's debatable as to whether or not the XUSB padctl
device should be a parent to the XUSB host/device-controller devices
(currently it isn't - it's just a PHY provider). But in the Type-C
case, it's an off-chip embedded controller that determines the
dual-role status of the Type-C port, so the above requirement doesn't
make sense at all.
My idea was to have the OTG/DRD controller explicitly specify its host
and device controllers, so in DT, something like:
otg-controller {
...
device-controller = usb_device;
host-controller = usb_host;
...
};
usb_device: usb-device@ {
...
};
usb_host: usb-host@... {
...
};
What do you think?
I agree that we need to support your use case but how to do it
is not yet clear to me.
In your above example the otg controller knows what are the host
and gadget controllers but the host/gadget devices don't
know who is their otg controller.
So the problem is that when usb_otg_register_hcd/gadget() is called
we need to get a handle to the otg controller.
One solution I see is to iterate over the registered otg_controller_list
and check if we match the host/gadget controller in there.
Then there is also a possibility that host/gadget controllers get
registered before the OTG controller. Then we can't know for sure if
the host/gadget controller was meant for dual-role operation or not
and it will resort to single role operation.
Any idea to prevent the above situation?
Maybe we need to add some logic in host/gadget cores to check if the port
is meant for dual-role use and defer probe if OTG controller is not yet
registered?
cheers,
-roger
--
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the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH v3 00/11] USB: OTG/DRD Core functionality
Hi Peter, On Mon, Jul 13, 2015 at 5:59 PM, Peter Chen peter.c...@freescale.com wrote: On Mon, Jul 13, 2015 at 12:14:43PM -0700, Andrew Bresticker wrote: Hi Roger, On Wed, Jul 8, 2015 at 3:19 AM, Roger Quadros rog...@ti.com wrote: 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. I'm wondering if the requirement that the OTG controller be the parent of the USB host/device-controllers makes sense. For some context, I'm working on adding dual-role support for Tegra210, specifically on a system with USB Type-C. On Tegra, the USB host-controller and USB device-controller are two separate IP blocks (XUSB host and XUSB device) with another, separate, IP block (XUSB padctl) for the USB PHY and OTG support. In the non-Type-C case, your OTG framework could work well, though it's debatable as to whether or not the XUSB padctl device should be a parent to the XUSB host/device-controller devices (currently it isn't - it's just a PHY provider). But in the Type-C case, it's an off-chip embedded controller that determines the dual-role status of the Type-C port, so the above requirement doesn't make sense at all. Hi Andrew, I think your problem is how to add your core driver to manage device and host functionality together, and once you find how (through padctl/type-c controller) to do it based on current code, it will be clear how to use roger proposal framework at that time. Most of current core drivers, we use extcon driver (through gpio) or USB vbus/id pin (through internal registers) to manager roles. Right, currently I'm modeling the Type-C controller as an extcon device and handle the role-changes in the core drivers, but that doesn't really make sense for the non-Type-C case where we use the XUSB padctl controller and need a full OTG state-machine. Roger's new OTG/DRD framework would fit my situation perfectly since it makes the host/device-controller drivers independent from all the OTG/role-changing logic. The only issue is the requirement that the OTG/DRD controller be the parent device of the host/device controllers. Thanks, Andrew -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH v3 00/11] USB: OTG/DRD Core functionality
On Tue, Jul 14, 2015 at 11:18:30AM -0700, Andrew Bresticker wrote: Hi Peter, On Mon, Jul 13, 2015 at 5:59 PM, Peter Chen peter.c...@freescale.com wrote: On Mon, Jul 13, 2015 at 12:14:43PM -0700, Andrew Bresticker wrote: Hi Roger, On Wed, Jul 8, 2015 at 3:19 AM, Roger Quadros rog...@ti.com wrote: 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. I'm wondering if the requirement that the OTG controller be the parent of the USB host/device-controllers makes sense. For some context, I'm working on adding dual-role support for Tegra210, specifically on a system with USB Type-C. On Tegra, the USB host-controller and USB device-controller are two separate IP blocks (XUSB host and XUSB device) with another, separate, IP block (XUSB padctl) for the USB PHY and OTG support. In the non-Type-C case, your OTG framework could work well, though it's debatable as to whether or not the XUSB padctl device should be a parent to the XUSB host/device-controller devices (currently it isn't - it's just a PHY provider). But in the Type-C case, it's an off-chip embedded controller that determines the dual-role status of the Type-C port, so the above requirement doesn't make sense at all. Hi Andrew, I think your problem is how to add your core driver to manage device and host functionality together, and once you find how (through padctl/type-c controller) to do it based on current code, it will be clear how to use roger proposal framework at that time. Most of current core drivers, we use extcon driver (through gpio) or USB vbus/id pin (through internal registers) to manager roles. Right, currently I'm modeling the Type-C controller as an extcon device and handle the role-changes in the core drivers, but that doesn't really make sense for the non-Type-C case where we use the XUSB padctl controller and need a full OTG state-machine. The full OTG FSM is only applied if your board needs it, you can disable it through dts. Jun [1] and Roger's patchset are for it. Roger's new OTG/DRD framework would fit my situation perfectly since it makes the host/device-controller drivers independent from all the OTG/role-changing logic. The only issue is the requirement that the OTG/DRD controller be the parent device of the host/device controllers. The core device is the parent for host/device device, the OTG core just use the pointer of it, Roger does an example using dwc3 [2]. [1] http://www.spinics.net/lists/linux-usb/msg127110.html [2] http://www.spinics.net/lists/linux-usb/msg126999.html -- Best Regards, Peter Chen -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH v3 00/11] USB: OTG/DRD Core functionality
Hi, On 10/07/15 10:58, Li Jun wrote: On Wed, Jul 08, 2015 at 01:19:26PM +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. xhci side of things for OTG/DRD use are already in v4.2 Do you have any plan to implement OTG(HNP) on some of your platforms based on this OTG core? Not yet but Joao Pinto was interested to implement full OTG for dwc3 controllers. Would you be interested to try out one of your platforms so that we can address any issues early? cheers, -roger Li Jun http://thread.gmane.org/gmane.linux.kernel/1923161 DWC3 controller and platform related patches are sent separately. Changelog: -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH v3 00/11] USB: OTG/DRD Core functionality
On Mon, Jul 13, 2015 at 01:24:05PM +0300, Roger Quadros wrote: Hi, On 10/07/15 10:58, Li Jun wrote: On Wed, Jul 08, 2015 at 01:19:26PM +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. xhci side of things for OTG/DRD use are already in v4.2 Do you have any plan to implement OTG(HNP) on some of your platforms based on this OTG core? Not yet but Joao Pinto was interested to implement full OTG for dwc3 controllers. Would you be interested to try out one of your platforms so that we can address any issues early? cheers, -roger Yes, I am considering to try out OTG on chipidea driver for FSL i.mx6x platform , which will based on your OTG core and my previous gadget update patchset. I will comment your patchset if find any issues. Since there is still much work to do to complete OTG HNP/SRP, so I assume this will not be done in a short time. Li Jun Li Jun http://thread.gmane.org/gmane.linux.kernel/1923161 DWC3 controller and platform related patches are sent separately. Changelog: -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH v3 00/11] USB: OTG/DRD Core functionality
On Mon, Jul 13, 2015 at 12:14:43PM -0700, Andrew Bresticker wrote:
Hi Roger,
On Wed, Jul 8, 2015 at 3:19 AM, Roger Quadros rog...@ti.com wrote:
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.
I'm wondering if the requirement that the OTG controller be the parent
of the USB host/device-controllers makes sense. For some context, I'm
working on adding dual-role support for Tegra210, specifically on a
system with USB Type-C. On Tegra, the USB host-controller and USB
device-controller are two separate IP blocks (XUSB host and XUSB
device) with another, separate, IP block (XUSB padctl) for the USB PHY
and OTG support. In the non-Type-C case, your OTG framework could
work well, though it's debatable as to whether or not the XUSB padctl
device should be a parent to the XUSB host/device-controller devices
(currently it isn't - it's just a PHY provider). But in the Type-C
case, it's an off-chip embedded controller that determines the
dual-role status of the Type-C port, so the above requirement doesn't
make sense at all.
Hi Andrew,
I think your problem is how to add your core driver to manage device and
host functionality together, and once you find how (through padctl/type-c
controller) to do it based on current code, it will be clear how to use roger
proposal framework at that time.
Most of current core drivers, we use extcon driver (through gpio) or USB
vbus/id pin (through internal registers) to manager roles.
My idea was to have the OTG/DRD controller explicitly specify its host
and device controllers, so in DT, something like:
otg-controller {
...
device-controller = usb_device;
host-controller = usb_host;
...
};
usb_device: usb-device@ {
...
};
usb_host: usb-host@... {
...
};
What do you think?
Thanks,
Andrew
--
Best Regards,
Peter Chen
--
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the body of a message to majord...@vger.kernel.org
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Re: [PATCH v3 00/11] USB: OTG/DRD Core functionality
Hi Roger,
On Wed, Jul 8, 2015 at 3:19 AM, Roger Quadros rog...@ti.com wrote:
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.
I'm wondering if the requirement that the OTG controller be the parent
of the USB host/device-controllers makes sense. For some context, I'm
working on adding dual-role support for Tegra210, specifically on a
system with USB Type-C. On Tegra, the USB host-controller and USB
device-controller are two separate IP blocks (XUSB host and XUSB
device) with another, separate, IP block (XUSB padctl) for the USB PHY
and OTG support. In the non-Type-C case, your OTG framework could
work well, though it's debatable as to whether or not the XUSB padctl
device should be a parent to the XUSB host/device-controller devices
(currently it isn't - it's just a PHY provider). But in the Type-C
case, it's an off-chip embedded controller that determines the
dual-role status of the Type-C port, so the above requirement doesn't
make sense at all.
My idea was to have the OTG/DRD controller explicitly specify its host
and device controllers, so in DT, something like:
otg-controller {
...
device-controller = usb_device;
host-controller = usb_host;
...
};
usb_device: usb-device@ {
...
};
usb_host: usb-host@... {
...
};
What do you think?
Thanks,
Andrew
--
To unsubscribe from this list: send the line unsubscribe linux-omap in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH v3 00/11] USB: OTG/DRD Core functionality
On Wed, Jul 08, 2015 at 01:19:26PM +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. xhci side of things for OTG/DRD use are already in v4.2 Do you have any plan to implement OTG(HNP) on some of your platforms based on this OTG core? Li Jun http://thread.gmane.org/gmane.linux.kernel/1923161 DWC3 controller and platform related patches are sent separately. Changelog: -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH v3 00/11] USB: OTG/DRD Core functionality
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. xhci side of things for OTG/DRD use are already in v4.2 http://thread.gmane.org/gmane.linux.kernel/1923161 DWC3 controller and platform related patches are sent separately. Changelog: - 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 *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, 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. 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. If drd_only parameter is 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
