linux-kernel - Re: [PATCH v5] usb: common: usb-conn-gpio: Set last role to unknown before initial detection

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Message-ID: <a86f3bd4-8c87-de67-bdb6-fbe88dc23a56@quicinc.com>
Date:   Tue, 30 May 2023 00:00:15 +0530
From:   Prashanth K <quic_prashk@...cinc.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5] usb: common: usb-conn-gpio: Set last role to unknown
 before initial detection



On 28-05-23 05:03 pm, Greg Kroah-Hartman wrote:
>>>> diff --git a/drivers/usb/common/usb-conn-gpio.c b/drivers/usb/common/usb-conn-gpio.c
>>>> index e20874c..30bdb81 100644
>>>> --- a/drivers/usb/common/usb-conn-gpio.c
>>>> +++ b/drivers/usb/common/usb-conn-gpio.c
>>>> @@ -257,6 +257,9 @@ static int usb_conn_probe(struct platform_device *pdev)
>>>>    	platform_set_drvdata(pdev, info);
>>>>    	device_set_wakeup_capable(&pdev->dev, true);
>>>> +	/* Set last role to unknown before performing the initial detection */
>>>> +	info->last_role = USB_ROLE_UNKNOWN;
>>>
>>> Shouldn't last_role have already been set to 0?  If so, why not just
>>> have this enum value be 0?
>> Last role would be 0 during first detection, that's the problem here.
>> During initial detection, if the the new role is detected as USB_ROLE_NONE
>> (0), then we wouldn't call the set_role(). But it should send the current
>> role to gadget after the inital detection.
> 
> So you are hoping that the old enum type is still assigned to 0?  That's
> brave, please make it explicit otherwise it's very hard to follow or
> ensure that this really will happen.  And most of all, document it so
> that that value remains 0 in the future, otherwise a list of enum types
> without explicit values are seen as if the values do not matter.
> 
> thanks,
> 
> greg k-h

So I think it would be better to add USB_ROLE_UNKNOWN towards the end of 
enum usb_role, so that we can avoid explicit declaration. Is that fine?

  enum usb_role {
  	USB_ROLE_NONE,
  	USB_ROLE_HOST,
  	USB_ROLE_DEVICE,
+	USB_ROLE_UNKNOWN,
   }

Thanks,
Prashanth K