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

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Message-ID: <2023052943-headfirst-satchel-6d90@gregkh>
Date:   Mon, 29 May 2023 20:01:03 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Prashanth K <quic_prashk@...cinc.com>
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 Tue, May 30, 2023 at 12:00:15AM +0530, Prashanth K wrote:
> 
> 
> 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,

Either is fine, be explicit, or not, just don't mix the two please.

thanks,

greg k-h