linux-kernel - Re: usb: common: usb-conn-gpio: Prevent bailing out if initial role is none

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Message-ID: <3f4ebebb-b1cb-27da-053f-146c8699c16e@quicinc.com>
Date:   Wed, 26 Jul 2023 15:25:03 +0530
From:   Prashanth K <quic_prashk@...cinc.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: usb: common: usb-conn-gpio: Prevent bailing out if initial role
 is none



On 25-07-23 09:04 pm, Greg Kroah-Hartman wrote:
> On Thu, Jul 06, 2023 at 03:40:58PM +0530, Prashanth K wrote:
>> Currently if we bootup a device without cable connected, then
>> usb-conn-gpio won't call set_role() since last_role is same as
>> current role. This happens because during probe last_role gets
>> initialised to zero.
>>
>> To avoid this, add a new flag initial_det in usb_conn_info,
>> which is used to prevent bailing out during init detection.
>>
>> Fixes: 4602f3bff266 ("usb: common: add USB GPIO based connection detection driver")
>> Signed-off-by: Prashanth K <quic_prashk@...cinc.com>
>> ---
>>   drivers/usb/common/usb-conn-gpio.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/common/usb-conn-gpio.c b/drivers/usb/common/usb-conn-gpio.c
>> index 766005d..46290ff 100644
>> --- a/drivers/usb/common/usb-conn-gpio.c
>> +++ b/drivers/usb/common/usb-conn-gpio.c
>> @@ -42,6 +42,7 @@ struct usb_conn_info {
>>   
>>   	struct power_supply_desc desc;
>>   	struct power_supply *charger;
>> +	bool initial_det;
> 
> What does "initial_det" mean?  Please document this better.
> 
Yea sure, will update that. It was supposed to mean initial_detection.
>>   };
>>   
>>   /*
>> @@ -86,11 +87,13 @@ static void usb_conn_detect_cable(struct work_struct *work)
>>   	dev_dbg(info->dev, "role %s -> %s, gpios: id %d, vbus %d\n",
>>   		usb_role_string(info->last_role), usb_role_string(role), id, vbus);
>>   
>> -	if (info->last_role == role) {
>> +	if (!info->initial_det && info->last_role == role) {
>>   		dev_warn(info->dev, "repeated role: %s\n", usb_role_string(role));
>>   		return;
>>   	}
>>   
>> +	info->initial_det = false;
>> +
>>   	if (info->last_role == USB_ROLE_HOST && info->vbus)
>>   		regulator_disable(info->vbus);
>>   
>> @@ -258,6 +261,7 @@ static int usb_conn_probe(struct platform_device *pdev)
>>   	device_set_wakeup_capable(&pdev->dev, true);
>>   
>>   	/* Perform initial detection */
>> +	info->initial_det = true;
> 
> What is protecting this from changing right after you test for it?
> 
> thanks,
> 
> greg k-h

Hi Greg, this variable is only used/changed by usb_conn_detect_cable() 
which is called in next line. So the chance of it changing is none.
Basically this initial_det flag points if its initial detection or not.
If yes, then prevent bailing out in usb_conn_detect_cable(). Please let 
me know if your comment was regarding something else.

Regards,
Prashanth K