linux-kernel - Re: [PATCH v2 1/5] usb: gadget: Add remote wakeup capable flag

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Message-ID: <Y8tIrx+F/4X9YyFT@rowland.harvard.edu>
Date:   Fri, 20 Jan 2023 21:06:39 -0500
From:   Alan Stern <stern@...land.harvard.edu>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Cc:     Elson Serrao <quic_eserrao@...cinc.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "balbi@...nel.org" <balbi@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "quic_wcheng@...cinc.com" <quic_wcheng@...cinc.com>,
        "quic_jackp@...cinc.com" <quic_jackp@...cinc.com>
Subject: Re: [PATCH v2 1/5] usb: gadget: Add remote wakeup capable flag

On Sat, Jan 21, 2023 at 02:02:36AM +0000, Thinh Nguyen wrote:
> On Fri, Jan 20, 2023, Alan Stern wrote:
> > A UDC design might have multiple versions, some supporting remote wakeup 
> > and others not.  But drivers generally use a single static 
> > usb_gadget_ops structure, and they don't modify it at runtime to account 
> > for hardware differences.  So if a single driver controls those multiple 
> > versions, you can't rely on the presence of gadget->ops->wakeup to 
> > indicate whether there actually is hardware remote wakeup support.
> > 
> > Ideally, the usb_gadget structure should have a wakeup_capable flag 
> > which the UDC driver would set appropriately (probably during its probe 
> > routine).
> > 
> 
> I was thinking that it can be handled by the
> usb_gadget_enable_remote_wakeup() so we can do away with the
> wakeup_capable flag.

usb_gadget_enable_remote_wakeup() gets called when the gadget or 
function is suspended, right?  But a gadget driver may want to know long 
before that whether the UDC supports remote wakeup, in order to set up 
its config descriptor correctly.

Alan Stern