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From:   Alexandru Gagniuc <alexandru.gagniuc@hp.com>
To:     stern@rowland.harvard.edu
Cc:     alexandru.gagniuc@hp.com, bjorn@mork.no, davem@davemloft.net,
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Subject: Re: [PATCH v2] r8152: Suspend USB device before shutdown when WoL is enabled
Date:   Thu, 10 Aug 2023 22:51:09 +0000
Message-Id: <20230810225109.13973-1-alexandru.gagniuc@hp.com>
In-Reply-To: <78e3aade-2a88-42f4-9991-8e245f3eb9b9@rowland.harvard.edu>
References: <78e3aade-2a88-42f4-9991-8e245f3eb9b9@rowland.harvard.edu>
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On Thu, Aug 10, 2023 at 01:34:39PM -0400, Alan Stern wrote:
> On Thu, Aug 10, 2023 at 04:22:16PM +0000, Alexandru Gagniuc wrote:
> > On Wed, Aug 02, 2023 at 11:23:46AM -0400, Alan Stern wrote:
> > >=20
> > > Indeed.  And I am asking how you can be sure the host controller driv=
er=20
> > > (or some other part of the software stack) doesn't have this bug.
> >=20
> > The only way that I have to show that is empirical. I observe that WoL =
from S5
> > does not work on a device with an r8153 chip. I apply the change, and v=
erify
> > that WoL from S5 now works in this scenario. What are you thinking of i=
n terms
> > of being sure no current or future bug exists?
>=20
> I was thinking that the host controller driver's shutdown method might=20
> turn off power to all of the ports.
>=20
> For example, in the ehci-hcd driver, ehci_shutdown() calls=20
> ehci_silence_controller(), which calls ehci_turn_off_all_ports().  I=20
> 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 stat=
e.

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 por=
ts.
The quirk appears to switch ports to EHCI mode, rather than turn off power.

Alex