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

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Date:   Fri, 26 May 2023 10:15:43 +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 25-05-23 10:04 pm, Greg Kroah-Hartman wrote:
> On Thu, May 25, 2023 at 02:23:45PM +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, added a new constant in enum usb_role, last_role
>> is set to USB_ROLE_UNKNOWN before performing initial detection.
>>
>> While at it, also handle default case for the usb_role switch
>> in cdns3 to avoid build warnings.
>>
>> Fixes: 4602f3bff266 ("usb: common: add USB GPIO based connection detection driver")
>> Signed-off-by: Prashanth K <quic_prashk@...cinc.com>
>> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
>> ---
>> v5: Update commit text to mention the changes made in cdns3 driver.
>> v4: Added Reviewed-by tag.
>> v3: Added a default case in drivers/usb/cdns3/core.c as pointed out by
>>      the test robot.
>> v2: Added USB_ROLE_UNKNWON to enum usb_role.
>>
>>   drivers/usb/cdns3/core.c           | 2 ++
>>   drivers/usb/common/usb-conn-gpio.c | 3 +++
>>   include/linux/usb/role.h           | 1 +
>>   3 files changed, 6 insertions(+)
>>
>> diff --git a/drivers/usb/cdns3/core.c b/drivers/usb/cdns3/core.c
>> index dbcdf3b..69d2921 100644
>> --- a/drivers/usb/cdns3/core.c
>> +++ b/drivers/usb/cdns3/core.c
>> @@ -252,6 +252,8 @@ static enum usb_role cdns_hw_role_state_machine(struct cdns *cdns)
>>   		if (!vbus)
>>   			role = USB_ROLE_NONE;
>>   		break;
>> +	default:
>> +		break;
> 
> No error if this happens?
It wouldn't come to default case in as no one sets the role to 
USB_ROLE_UNKNOWN in cdns3 driver. Moreover it would work the same
without the default case also (we have added it just to address a 
warning pointed out be test-robot).
> 
>>   	}
>>   
>>   	dev_dbg(cdns->dev, "role %d -> %d\n", cdns->role, role);
>> 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.

if (info->last_role == role) {
		dev_warn(info->dev, "repeated role: %s\n", usb_role_string(role));
		return;
	}
> 
> 
>> +
>>   	/* Perform initial detection */
>>   	usb_conn_queue_dwork(info, 0);
>>   
>> diff --git a/include/linux/usb/role.h b/include/linux/usb/role.h
>> index b5deafd..221d462 100644
>> --- a/include/linux/usb/role.h
>> +++ b/include/linux/usb/role.h
>> @@ -8,6 +8,7 @@
>>   struct usb_role_switch;
>>   
>>   enum usb_role {
>> +	USB_ROLE_UNKNOWN = -1,
> 
> Why is this explicitly set to a value?  What is magic about -1?  Why not
> 0x42?  Or something else?  Or as I mention above, 0?
> I just chose -1 as the currently 0,1,2 are used for NONE, Device and 
Host roles. Didn't make the USB_ROLE_UNKNOWN = 0 because i didn't want 
to break the existing logic in other drivers. Do you have any 
suggestion? Please let me know.

Thanks,
Prashanth K