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

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Message-ID: <Y8tGAXbKDtzmW8+E@rowland.harvard.edu>
Date:   Fri, 20 Jan 2023 20:55:13 -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 12:21:10AM +0000, Thinh Nguyen wrote:
> The way gadget->rw_capable is named and described, it's a capability
> flag. That is, its value shouldn't change from the user config. Perhaps
> we don't need that in the usb_gadget, and we can have something that
> looks like this:
> 
> if (gadget->ops->wakeup && (c->bmAttributes & USB_CONFIG_ATT_WAKEUP))
> 	usb_gadget_enable_remote_wakeup(g);
> else
> 	usb_gadget_disable_remote_wakeup(g);
> 
> The setting of the remote wakeup configuration can be tracked internally
> by the dwc3 driver based on the usb_gadget_enable_remote_wakeup call.

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).

Alan Stern