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From:   "Gagniuc, Alexandru" <alexandru.gagniuc@hp.com>
To:     Alan Stern <stern@rowland.harvard.edu>
CC:     "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "edumazet@google.com" <edumazet@google.com>,
        "kuba@kernel.org" <kuba@kernel.org>,
        "pabeni@redhat.com" <pabeni@redhat.com>,
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        "bjorn@mork.no" <bjorn@mork.no>,
        "svenva@chromium.org" <svenva@chromium.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Zhang, Eniac" <eniac-xw.zhang@hp.com>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH v2] r8152: Suspend USB device before shutdown when WoL is
 enabled
Thread-Topic: [PATCH v2] r8152: Suspend USB device before shutdown when WoL is
 enabled
Thread-Index: AQHZumfGWALIKL1Qf0uRlSRmGE3IR6/BawiAgBXCwgU=
Date:   Wed, 2 Aug 2023 14:56:43 +0000
Message-ID: <SJ0PR84MB2088F20891376312BA8D550A8F0BA@SJ0PR84MB2088.NAMPRD84.PROD.OUTLOOK.COM>
References: <2c12d7a0-3edb-48b3-abf7-135e1a8838ca@rowland.harvard.edu>
 <20230719173756.380829-1-alexandru.gagniuc@hp.com>
 <3c4fd3d8-2b0b-492e-aacc-afafcea98417@rowland.harvard.edu>
In-Reply-To: <3c4fd3d8-2b0b-492e-aacc-afafcea98417@rowland.harvard.edu>
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On Wed, Jul 19, 2023 at 02:36:25PM -0400, Alan Stern wrote:=0A> On Wed, Jul=
 19, 2023 at 05:37:56PM +0000, Alexandru Gagniuc wrote:=0A> > For Wake-on-L=
AN to work from S5 (shutdown), the USB link must be put=0A> > in U3 state. =
If it is not, and the host "disappears", the chip will=0A> > no longer resp=
ond to WoL triggers.=0A> >=20=0A> > To resolve this, add a notifier block a=
nd register it as a reboot=0A> > notifier. When WoL is enabled, work throug=
h the usb_device struct to=0A> > get to the suspend function. Calling this =
function puts the link in=0A> > the correct state for WoL to function.=0A>=
=20=0A> How do you know that the link will _remain_ in the correct state?=
=0A=0AThe objective is to get to xhci_set_link_state() with the USB_SS_PORT=
_LS_U3=0Aargument. This is achieved through usb_port_suspend() in drivers/u=
sb/host/hub.c,=0Aand the function is implemented in drivers/usb/host/xhci-h=
ub.c.=0A=0AThis is the only path in the kernel that I am aware of for setti=
ng the U3 link=0Astate. Given that it is part of the USB subsystem, I am fa=
irly confident it will=0Ashow consistent behavior across platforms.=0A=20=
=0A> That is, how do you know that the shutdown processing for the USB host=
=20=0A> controller won't disable the link entirely, thereby preventing WoL =
from=20=0A> working?=0A=0AWe are talking to the USB hub in order to set the=
 link state. I don't see how=0Aspecifics of the host controller would influ=
ence behavior. I do expect a=0Acontroller which advertises S4/S5 in /proc/a=
cpi/wakeup to not do anything that=0Awould sabotage this capability. Disabl=
ing the link entirely would probalby=0Aviolate that promise.=0A=0AThink of =
USB-C docks with a power button showing up as a HID class. The scenario=0Ah=
erein would disable the power button. I would take that to be a bug in the =
host=0Acontroller driver if the S4/S5 capability is advertised.=0A=0AAlex=
=0A=0AP.S. I sincerely apologize for the delay in my reply. The corporate e=
mail servers here=0Ahave "difficulties" with plaintext and  interleaved rep=
lies.=0A