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

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Message-ID: <20230121021219.udgpwt7tv7dfr3jk@synopsys.com>
Date:   Sat, 21 Jan 2023 02:12:32 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Alan Stern <stern@...land.harvard.edu>
CC:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        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 Fri, Jan 20, 2023, Alan Stern wrote:
> 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.
> 

No, this is to be called during set configuration. If the configuration
doesn't support remote wakeup, the device should not be able to send
remote wakeup.

BR,
Thinh