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

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Message-ID: <YxdNKx1OFKsgBUBu@black.fi.intel.com>
Date:   Tue, 6 Sep 2022 16:37:47 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Kai-Heng Feng <kai.heng.feng@...onical.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 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.

> 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.

> > 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? ;-)