linux-kernel - Re: [PATCH] thunderbolt: Resume PCIe bridges after switch is found on AMD USB4 controller

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Date:   Tue, 6 Sep 2022 22:29:03 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     andreas.noever@...il.com, michael.jamet@...el.com,
        YehezkelShB@...il.com, sanju.mehta@....com,
        mario.limonciello@....com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] thunderbolt: Resume PCIe bridges after switch is found on
 AMD USB4 controller

On Tue, Sep 6, 2022 at 9:37 PM Mika Westerberg
<mika.westerberg@...ux.intel.com> wrote:
>
> On Tue, Sep 06, 2022 at 08:57:20PM +0800, Kai-Heng Feng wrote:
> > On Mon, Sep 5, 2022 at 11:34 PM Mika Westerberg
> > <mika.westerberg@...ux.intel.com> wrote:
> > >
> > > On Mon, Sep 05, 2022 at 11:21:36PM +0800, Kai-Heng Feng wrote:
> > > > > Hmm, so you see the actual hotplug but the tunneled PCIe link may not be
> > > > > detected? Does the PCIe "Card Present" (or Data Link Layer Active)
> > > > > status change at all or is it always 0?
> > > >
> > > > It changes only after tb_switch_add() is called.
> > >
> > > I doubt tb_switch_add() does anything but instead it is the established
> > > PCIe tunnel that then shows up as it toggles the Card Present bit or so.
> > > But that should also trigger PME if the root port is in D3 so you should
> > > see this wake if everything works accordingly (unless I'm missing
> > > something).
> >
> > You are right. Sometimes it may still fail to detect hotplugged device
> > right after tb_switch_add().
> > At which point PCIe tunnels are established? Is it after tb_scan_port()?
>
> They are established when userspace writes "1" to ../authorized of the
> device (not automatically).
>
> On Ubuntu that's boltd that handles this so you may need to disable it
> before you do the experiment.

In the dmesg it was disabled and "authorized" was 0 originally.

>
> > I found that it's cleaner to wakeup hotplug ports via iterating device
> > link consumers at the end of tb_scan_port().
> >
> > According to your commit b2be2b05cf3b1c7b499d3b05decdcc524879fea7
> > ("thunderbolt: Create device links from ACPI description"), it states
> > "The _DSD can be added to tunneled USB3 and PCIe ports, and is needed to
> > make sure the USB4 NHI is resumed before any of the tunneled ports so
> > the protocol tunnels get established properly before the actual port
> > itself is resumed. Othwerwise the USB/PCI core find the link may not be
> > established and starts tearing down the device stack."
> >
> > So isn't waking them up a logical thing to do here?
>
> No they should wake up themselves.

OK.

>
> > > So if you do this:
> > >
> > > 1. Boot the system up, nothing connected
> > > 2. Plug in the TBT/USB4 device but do not authorize the PCIe tunnel
> > > 3. Wait for the TBT/USB4 domain to enter sleep (runtime suspend)
> > > 4. Authorize the PCIe tunnel
> > >
> > >   # echo 1 > .../authorized
> > >
> > > The established PCIe tunnel should trigger PME and the root port then
> > > should be able to detect the PCIe link. Can you add full dmesg with
> > > "thunderbolt.dyndbg=+p" in the command line to the bug?
> >
> > dmesg attached. Unfortunately there's no PME.
>
> Hmm, attached to where? Forgot to attach? ;-)

Oops, it's attached to the Bugzilla now.

Kai-Heng