linux-kernel - Re: [PATCH] Supporting wake on DP hot events behind TBT/USB4 routers

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Date:   Wed, 3 Aug 2022 18:57:42 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Benson Leung <bleung@...gle.com>
Cc:     Rajat Khandelwal <rajat.khandelwal@...el.com>,
        andreas.noever@...il.com, michael.jamet@...el.com,
        YehezkelShB@...il.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, pmalani@...gle.com
Subject: Re: [PATCH] Supporting wake on DP hot events behind TBT/USB4 routers

Hi Benson,

On Wed, Aug 03, 2022 at 08:15:49AM -0700, Benson Leung wrote:
> Hi Mika,
> 
> On Tue, Aug 2, 2022 at 10:37 PM Mika Westerberg
> <mika.westerberg@...ux.intel.com> wrote:
> >
> > Hi,
> >
> > On Wed, Aug 03, 2022 at 06:31:39AM +0530, Rajat Khandelwal wrote:
> > > Current implementation doesn't allow user to go into system suspend
> > > and simultaneously project the screen on an external display connected
> > > to a TBT/USB4 device. This patch enables this feature.
> > >
> > > Let me know what you think about this.
> >
> > Please prefix patches to follow the sybsystem style. For Thunderbolt it
> > should be "thunderbolt: ....".
> >
> > This will cause any monitor plug to wake up the system and I'm not sure
> > we want that, at least to be default behaviour. If you have a regular
> > Type-C (non-USB4/TBT) dock and you plug in a monitor to that, does it
> > wake up?
> 
> Speaking for Google and our ChromeOS USB-C policy, yes, if the host is
> in S0iX or S3, an already attached USB-C docking station in DP Alt
> Mode will respond to a display attach via HPD via an Alert message in
> USB PD. We called this feature wake-on-dock.
> 
> We implemented wake-on-dock for DP Alt Mode in the EC, since our EC
> handles USB PD anyway, and is handling the PD Alert message which
> contains the HPD status.
> 
> However, when the dock supports USB4 or Thunderbolt, those modes don't
> involve USB PD for device attach, so our EC doesn't have the role of
> waking the system, so something else on the system must, which is this
> feature being discussed.

Okay understood. Thanks for explaining!