linux-kernel - Re: [PATCH] USB: core: Enable root_hub's remote wakeup for wakeup sources

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Message-ID: <2f583e59-5322-4cac-aaaf-02163084c32c@rowland.harvard.edu>
Date: Fri, 31 Jan 2025 10:17:27 -0500
From: Alan Stern <stern@...land.harvard.edu>
To: Huacai Chen <chenhuacai@...ngson.cn>
Cc: Huacai Chen <chenhuacai@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] USB: core: Enable root_hub's remote wakeup for wakeup
 sources

On Fri, Jan 31, 2025 at 06:06:30PM +0800, Huacai Chen wrote:
> Now we only enable the remote wakeup function for the USB wakeup source
> itself at usb_port_suspend(). But on pre-XHCI controllers this is not
> enough to enable the S3 wakeup function for USB keyboards,

Why do you say this?  It was enough on my system with an EHCI/UHCI 
controller when I wrote that code.  What hardware do you have that isn't 
working?

>  so we also
> enable the root_hub's remote wakeup (and disable it on error). Frankly
> this is unnecessary for XHCI, but enable it unconditionally make code
> simple and seems harmless.

This does not make sense.  For hubs (including root hubs), enabling 
remote wakeup means that the hub will generate a wakeup request when 
there is a connect, disconnect, or over-current change.  That's not what 
you want to do, is it?  And it has nothing to do with how the hub 
handles wakeup requests received from downstream devices.

You need to explain what's going on here in much more detail.  What 
exactly is going wrong, and why?  What is the hardware actually doing, 
as compared to what we expect it to do?

Alan Stern