netdev - Re: [PATCH v2] r8152: Suspend USB device before shutdown when WoL is enabled

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Date: Thu, 10 Aug 2023 21:51:11 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Alexandru Gagniuc <alexandru.gagniuc@...com>
Cc: bjorn@...k.no, davem@...emloft.net, edumazet@...gle.com,
  eniac-xw.zhang@...com, hayeswang@...ltek.com, jflf_kernel@....com,
  kuba@...nel.org, linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
  netdev@...r.kernel.org, pabeni@...hat.com, stable@...r.kernel.org,
  svenva@...omium.org
Subject: Re: [PATCH v2] r8152: Suspend USB device before shutdown when WoL is
 enabled

On Thu, Aug 10, 2023 at 10:51:09PM +0000, Alexandru Gagniuc wrote:
> On Thu, Aug 10, 2023 at 01:34:39PM -0400, Alan Stern wrote:
> > I was thinking that the host controller driver's shutdown method might 
> > turn off power to all of the ports.
> > 
> > For example, in the ehci-hcd driver, ehci_shutdown() calls 
> > ehci_silence_controller(), which calls ehci_turn_off_all_ports().  I 
> > don't know if xhci-hcd does anything similar.
> 
> EHCI is a different beast. I don't think EHCI (USB2.0) has the U3 link state.

USB-2 doesn't have link states, but it does have the notion of a 
downstream port being suspended, which is effectively the same as U3.

> The equivalent for would be xhci_shutdown(). It makes a call to
> usb_disable_xhci_ports() for XHCI_SPURIOUS_REBOOT quirk. As I have not
> encountered it, I don't know how it will affect the link state of other ports.
> The quirk appears to switch ports to EHCI mode, rather than turn off power.

All right.  The important point is that the patch works for your 
situation.  I was just trying to find out how much thought you had given 
to the possibilities other people might face, if their systems aren't 
quite the same as yours.

Alan Stern