linux-kernel - Re: [PATCH v2 4/4] usb: dwc3: Workaround for super-speed host on dra7 in dual-role mode

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Date:   Sat, 25 Feb 2017 12:50:03 +0900
From:   Chanwoo Choi <cwchoi00@...il.com>
To:     Roger Quadros <rogerq@...com>
Cc:     Vivek Gautam <vivek.gautam@...eaurora.org>, balbi@...nel.org,
        Chanwoo Choi <cw00.choi@...sung.com>,
        linux-usb@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] usb: dwc3: Workaround for super-speed host on dra7
 in dual-role mode

2017-02-25 12:46 GMT+09:00 Chanwoo Choi <cwchoi00@...il.com>:
> Hi,
>
> 2017-02-24 21:02 GMT+09:00 Roger Quadros <rogerq@...com>:
>> +Chanwoo
>>
>> Hi Vivek,
>>
>> On 23/02/17 10:34, Vivek Gautam wrote:
>>>
>>>
>>> On 02/16/2017 06:36 PM, Roger Quadros wrote:
>>>> dra7 OTG core limits the host controller to USB2.0 (high-speed) mode
>>>> when we're operating in dual-role.
>>>>
>>>> We work around that by bypassing the OTG core and reading the
>>>> extcon framework directly for ID/VBUS events.
>>>>
>>>> Signed-off-by: Roger Quadros <rogerq@...com>
>>>> ---
>>>>   Documentation/devicetree/bindings/usb/dwc3.txt |   2 +
>>>>   drivers/usb/dwc3/core.c                        | 169 ++++++++++++++++++++++++-
>>>>   drivers/usb/dwc3/core.h                        |   5 +
>>>>   3 files changed, 170 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/usb/dwc3.txt b/Documentation/devicetree/bindings/usb/dwc3.txt
>>>> index e3e6983..9955c0d 100644
>>>> --- a/Documentation/devicetree/bindings/usb/dwc3.txt
>>>> +++ b/Documentation/devicetree/bindings/usb/dwc3.txt
>>>> @@ -53,6 +53,8 @@ Optional properties:
>>>>    - snps,quirk-frame-length-adjustment: Value for GFLADJ_30MHZ field of GFLADJ
>>>>       register for post-silicon frame length adjustment when the
>>>>       fladj_30mhz_sdbnd signal is invalid or incorrect.
>>>> + - extcon: phandle to the USB connector extcon device. If present, extcon
>>>> +    device will be used to get USB cable events instead of OTG controller.
>>>>      - <DEPRECATED> tx-fifo-resize: determines if the FIFO *has* to be reallocated.
>>>>   diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
>>>> index 619fa7c..b02d911 100644
>>>> --- a/drivers/usb/dwc3/core.c
>>>> +++ b/drivers/usb/dwc3/core.c
>>>
>>> [snip]
>>>
>>>> @@ -1587,6 +1727,14 @@ static int dwc3_probe(struct platform_device *pdev)
>>>>         dwc3_get_properties(dwc);
>>>>   +    if (dev->of_node) {
>>>> +        if (of_property_read_bool(dev->of_node, "extcon"))
>>>> +            dwc->edev = extcon_get_edev_by_phandle(dev, 0);
>>>
>>> Don't we want separate edev's for vbus and id ?
>>> One can have separate pins connected to them and in that case
>>> we can't get the events out of one pin only.
>>
>> Is such kind of hardware really there? Ideally one extcon device
>> represents one connector. So VBUS and ID events of a single USB
>> port should come on one extcon device.
>> If it doesn't then you need to fix your platforms extcon driver
>> so that it does.
>> Chanwoo can correct me if I'm wrong on this understanding.
>>
>> Currently, if VBUS and ID come on GPIOs the extcon-usb-gpio driver
>> takes care of both.
>
> Basically, one extcon device driver can support the multiple
> external connectors if the detection h/w or port is same.
>
> One extcon device with extcon-usb-gpio.c can support the detection
> of both ID and VBUS.
>
> But, if there is any issue of h/w schematic, we need to consider
> how to use the extcon device.

Additionally, the extcon-usb-gpio.c use the two gpio pins
to detect both ID and VBUS pins. We can check it on documentation[1]
of extcon-usb-gpio driver.

[1] https://git.kernel.org/cgit/linux/kernel/git/chanwoo/extcon.git/tree/Documentation/devicetree/bindings/extcon/extcon-usb-gpio.txt


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics