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Message-ID: <574599E4.3090302@ti.com>
Date: Wed, 25 May 2016 15:26:12 +0300
From: Roger Quadros <rogerq@...com>
To: Jun Li <jun.li@....com>, Peter Chen <hzpeterchen@...il.com>
CC: "peter.chen@...escale.com" <peter.chen@...escale.com>,
"balbi@...nel.org" <balbi@...nel.org>,
"tony@...mide.com" <tony@...mide.com>,
"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
"mathias.nyman@...ux.intel.com" <mathias.nyman@...ux.intel.com>,
"Joao.Pinto@...opsys.com" <Joao.Pinto@...opsys.com>,
"sergei.shtylyov@...entembedded.com"
<sergei.shtylyov@...entembedded.com>,
"jun.li@...escale.com" <jun.li@...escale.com>,
"grygorii.strashko@...com" <grygorii.strashko@...com>,
"yoshihiro.shimoda.uh@...esas.com" <yoshihiro.shimoda.uh@...esas.com>,
"robh@...nel.org" <robh@...nel.org>,
"nsekhar@...com" <nsekhar@...com>, "b-liu@...com" <b-liu@...com>,
"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v8 08/14] usb: otg: add OTG/dual-role core
On 25/05/16 06:19, Jun Li wrote:
>
>
>> -----Original Message-----
>> From: Peter Chen [mailto:hzpeterchen@...il.com]
>> Sent: Wednesday, May 25, 2016 10:44 AM
>> To: Roger Quadros <rogerq@...com>
>> Cc: peter.chen@...escale.com; balbi@...nel.org; tony@...mide.com;
>> gregkh@...uxfoundation.org; dan.j.williams@...el.com;
>> mathias.nyman@...ux.intel.com; Joao.Pinto@...opsys.com;
>> sergei.shtylyov@...entembedded.com; jun.li@...escale.com;
>> grygorii.strashko@...com; yoshihiro.shimoda.uh@...esas.com;
>> robh@...nel.org; nsekhar@...com; b-liu@...com; linux-usb@...r.kernel.org;
>> linux-omap@...r.kernel.org; linux-kernel@...r.kernel.org;
>> devicetree@...r.kernel.org
>> Subject: Re: [PATCH v8 08/14] usb: otg: add OTG/dual-role core
>>
>> On Tue, May 24, 2016 at 12:45:46PM +0300, Roger Quadros wrote:
>>> Hi Peter,
>>>
>>> I have one question here. Please see below.
>>>
>>> On 13/05/16 13:03, Roger Quadros wrote:
>>>> It provides APIs for the following tasks
>>>>
>>>> - Registering an OTG/dual-role capable controller
>>>> - Registering Host and Gadget controllers to OTG core
>>>> - Providing inputs to and kicking the OTG state machine
>>>>
>>>> Provide a dual-role device (DRD) state machine.
>>>> DRD mode is a reduced functionality OTG mode. In this mode we don't
>>>> support SRP, HNP and dynamic role-swap.
>>>>
>>>> In DRD operation, the controller mode (Host or Peripheral) is
>>>> decided based on the ID pin status. Once a cable plug (Type-A or
>>>> Type-B) is attached the controller selects the state and doesn't
>>>> change till the cable in unplugged and a different cable type is
>>>> inserted.
>>>>
>>>> As we don't need most of the complex OTG states and OTG timers we
>>>> implement a lean DRD state machine in usb-otg.c.
>>>> The DRD state machine is only interested in 2 hardware inputs 'id'
>>>> and 'b_sess_vld'.
>>>>
>>>> Signed-off-by: Roger Quadros <rogerq@...com>
>>>> ---
>>>> drivers/usb/common/Makefile | 2 +-
>>>> drivers/usb/common/usb-otg.c | 1042
>> ++++++++++++++++++++++++++++++++++++++++++
>>>> drivers/usb/core/Kconfig | 4 +-
>>>> include/linux/usb/gadget.h | 2 +
>>>> include/linux/usb/hcd.h | 1 +
>>>> include/linux/usb/otg-fsm.h | 7 +
>>>> include/linux/usb/otg.h | 154 ++++++-
>>>> 7 files changed, 1206 insertions(+), 6 deletions(-) create mode
>>>> 100644 drivers/usb/common/usb-otg.c
>>>>
>>>
>>> <snip>
>>>
>>>> +
>>>> +/**
>>>> + * usb_otg_register() - Register the OTG/dual-role device to OTG
>>>> +core
>>>> + * @dev: OTG/dual-role controller device.
>>>> + * @config: OTG configuration.
>>>> + *
>>>> + * Registers the OTG/dual-role controller device with the USB OTG
>> core.
>>>> + *
>>>> + * Return: struct usb_otg * if success, ERR_PTR() if error.
>>>> + */
>>>> +struct usb_otg *usb_otg_register(struct device *dev,
>>>> + struct usb_otg_config *config) {
>>>> + struct usb_otg *otg;
>>>> + struct otg_wait_data *wait;
>>>> + int ret = 0;
>>>> +
>>>> + if (!dev || !config || !config->fsm_ops)
>>>> + return ERR_PTR(-EINVAL);
>>>> +
>>>> + /* already in list? */
>>>> + mutex_lock(&otg_list_mutex);
>>>> + if (usb_otg_get_data(dev)) {
>>>> + dev_err(dev, "otg: %s: device already in otg list\n",
>>>> + __func__);
>>>> + ret = -EINVAL;
>>>> + goto unlock;
>>>> + }
>>>> +
>>>> + /* allocate and add to list */
>>>> + otg = kzalloc(sizeof(*otg), GFP_KERNEL);
>>>> + if (!otg) {
>>>> + ret = -ENOMEM;
>>>> + goto unlock;
>>>> + }
>>>> +
>>>> + otg->dev = dev;
>>>> + otg->caps = config->otg_caps;
>>>
>>> Here, we should be checking if user needs to disable any OTG features.
>>> So,
>>>
>>> if (dev->of_node)
>>> of_usb_update_otg_caps(dev->of_node, &otg->caps);
>>>
>>> Do you agree?
>>> This means we need to change otg->caps from 'struct usb_otg_caps *caps;'
>>> to 'struct usb_otg_caps caps;' so that we can modify the local copy
>>> instead of the one passed by the OTG controller.
>>
>> Why can't modify the one from OTG controller directly?
>
> Yes, if user wants to disable any OTG features, this should have been
> done in 'config->otg_caps', if not, 'config->otg_caps' from controller
> driver is invalid and making no sense.
I've tried to why to Peter's mail.
>
>>
>>>
>>> We can also move of_usb_update_otg_caps() to otg.h.
>>>
>>> We will also need to modify the udc-core code so that it sets
>>> gadget->otg_caps to the modified otg_caps from the OTG core. This will
>>> ensure that the right OTG descriptors are sent.
>>>
>>> So we will have to introduce an API.
>>>
>>> struct usb_otg_caps *usb_otg_get_otg_caps(struct device *otg_dev)
>>>
>>> And in udc-core.c,
>>>
>>> static int udc_bind_to_driver(struct usb_udc *udc, struct
>>> usb_gadget_driver *driver) { ..
>>> ret = driver->bind(udc->gadget, driver);
>>> if (ret)
>>> goto err1;
>>>
>>> /* If OTG, the otg core starts the UDC when needed */
>>> if (udc->gadget->otg_dev) {
>>> + udc->gadget->is_otg = true;
>>
>> gadget->is_otg is only set to true if fully OTG is supported and it
>> needs to send OTG descriptors at this case. DRD devices should not send
>> OTG descriptors.
>>
>>> + udc->gadget->otg_caps = usb_otg_get_otg_caps(udc->gadget-
>>> otg_dev);
>>
>> Getting otg capabilities should be prior to driver->bind since
>> usb_otg_descriptor_init is called at that. Besides, Gadget driver may be
>> probed before otg driver is registered
>>
>> I am wonder if we can implement defer probe for gadget/udc/host driver if
>> otg driver is not probed, in that case, some designs can be simpler like
>> wait list in otg driver.
>
> I even don't see much benefit of this kind of random order of OTG/HCD/GADGET
> registration, anyway OTG register can be done firstly.
You cannot control the order in systems where all 3 are implemented by separate
hardware modules. We have to consider that they can be registered
in any order and make sure it works.
returning -EPROBE_DEFER in usb_otg_add_gadget_udc()/usb_otg_add_hcd() if OTG
controller driver is not yet probed makes perfect sense and is the way to solve
this dependency issue.
> HCD and GADGET are both separated drivers, but OTG is newly added
> and what we need is just a registration in controller driver.
How do you solve the problem when host registers before OTG? I tried to solve it
using the wait_list in usb-otg.c. The other alternative is -EPROBE_DEFER during
usb_otg_add_hcd/udc().
--
cheers,
-roger
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