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

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Message-ID: <CAFp+6iHgnndNxOAHJL2123yGVAKX1DRB5-K=qmBoQHTMkxpXTg@mail.gmail.com>
Date:   Tue, 28 Feb 2017 19:24:15 +0530
From:   Vivek Gautam <vivek.gautam@...eaurora.org>
To:     cwchoi00@...il.com
Cc:     Roger Quadros <rogerq@...com>, Felipe Balbi <balbi@...nel.org>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Linux USB Mailing List <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

On Sat, Feb 25, 2017 at 9:20 AM, Chanwoo Choi <cwchoi00@...il.com> wrote:
> 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.

Right, i see it now. One edev for one connector.

>>> 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

Thanks Chanwoo, i understand it now. The extcon-usb-gpio supports
both vbus and id gpio, and updates the state of the edev likewise.

>
> --
> Best Regards,
> Chanwoo Choi
> Samsung Electronics
> --
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regards
Vivek
-- 
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