linux-kernel - Re: [PATCH v5 10/13] usb: dwc3: Registering a role switch in the DRD code.

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Date:   Fri, 12 Apr 2019 09:23:42 +0800
From:   Chen Yu <chenyu56@...wei.com>
To:     John Stultz <john.stultz@...aro.org>
CC:     <liuyu712@...ilicon.com>,
        Linux USB List <linux-usb@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, lkml <linux-kernel@...r.kernel.org>,
        "Zhuangluan Su" <suzhuangluan@...ilicon.com>,
        Kongfei <kongfei@...ilicon.com>, <wanghu17@...ilicon.com>,
        butao <butao@...ilicon.com>, <chenyao11@...wei.com>,
        <fangshengzhou@...ilicon.com>,
        Li Pengcheng <lipengcheng8@...wei.com>,
        <songxiaowei@...ilicon.com>, YiPing Xu <xuyiping@...ilicon.com>,
        <xuyoujun4@...wei.com>, Yudongbin <yudongbin@...ilicon.com>,
        Zang Leigang <zangleigang@...ilicon.com>,
        Jun Li <lijun.kernel@...il.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Subject: Re: [PATCH v5 10/13] usb: dwc3: Registering a role switch in the DRD
 code.

Hi John,

On 2019/4/12 8:48, John Stultz wrote:
> On Thu, Mar 28, 2019 at 9:14 PM Yu Chen <chenyu56@...wei.com> wrote:
>>
>> The Type-C drivers use USB role switch API to inform the
>> system about the negotiated data role, so registering a role
>> switch in the DRD code in order to support platforms with
>> USB Type-C connectors.
>>
> 
> Hey Yu Chen!
>   Thanks so much for sending these patches out!  I have run into some
> troubles on bootup where things aren't working properly at first, that
> seem to be due to state initialization races.  In chasing those down,
> I've found some other quirks I wanted to bring up.
> 
>> --- a/drivers/usb/dwc3/drd.c
>> +++ b/drivers/usb/dwc3/drd.c
>> @@ -479,6 +479,43 @@ static struct extcon_dev *dwc3_get_extcon(struct dwc3 *dwc)
>>         return edev;
>>  }
>>
>> +static int dwc3_usb_role_switch_set(struct device *dev, enum usb_role role)
>> +{
>> +       struct dwc3 *dwc = dev_get_drvdata(dev);
>> +       u32 mode;
>> +
>> +       switch (role) {
>> +       case USB_ROLE_HOST:
>> +               mode = DWC3_GCTL_PRTCAP_HOST;
>> +               break;
>> +       case USB_ROLE_DEVICE:
>> +               mode = DWC3_GCTL_PRTCAP_DEVICE;
>> +               break;
>> +       default:
>> +               if (dwc->role_switch_default_mode == USB_DR_MODE_HOST)
>> +                       mode = DWC3_GCTL_PRTCAP_HOST;
>> +               else
>> +                       mode = DWC3_GCTL_PRTCAP_DEVICE;
>> +               break;
>> +       }
>> +
>> +       dwc3_set_mode(dwc, mode);
>> +       return 0;
>> +}
>> +
>> +static enum usb_role dwc3_usb_role_switch_get(struct device *dev)
>> +{
>> +       struct dwc3 *dwc = dev_get_drvdata(dev);
>> +       unsigned long flags;
>> +       enum usb_role role;
>> +
>> +       spin_lock_irqsave(&dwc->lock, flags);
>> +       role = dwc->current_otg_role;
>> +       spin_unlock_irqrestore(&dwc->lock, flags);
>> +
>> +       return role;
>> +}
>> +
> 
> So the two functions above are a bit asymmetric.  The
> dwc3_usb_role_switch_set() can put the device into host or device
> mode, which eventually sets the current_dr_role value.  However on the
> dwc3_usb_role_switch_get() we return the current_otg_role value.
> current_otg_role isn't set unless current_dr_role is
> DWC3_GCTL_PRTCAP_OTG, which doesn't seem to happen here.
> 
> I suspect in dwc3_usb_role_switch_get() we should return
> current_dr_role, unless current_dr_role==DWC3_GCTL_PRTCAP_OTG, in
> which case we'd want to return current_otg_role.
> 
> Does that make sense?
> 
Yes, you are right! The dwc3_usb_role_switch_get() should return current_dr_role
. Actually if we register the dwc3_role_switch, the current_dr_role would not be DWC3_GCTL_PRTCAP_OTG.
> Nothing really actually use this dwc3_usb_role_switch_get() yet, so
> this was easy to overlook, and I only caught it as I was trying to
> debug some of the initialization races.
> 
> thanks
> -john
> 
> .
>