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

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Date:   Mon, 5 Sep 2022 23:24:26 +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 Mon, Sep 5, 2022 at 9:18 PM Mika Westerberg
<mika.westerberg@...ux.intel.com> wrote:
>
> Hi,
>
> On Mon, Sep 05, 2022 at 10:50:33AM +0300, Mika Westerberg wrote:
> > > Yes those root ports are resumed to D0 when something is plugged. They
> > > however fail to detect any externel PCIe devices.
> >
> > 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?
>
> I wonder if we are simply missing the required delays here? Looking at
> the lspci dump in the bugzilla you refer the root port 03.1 supports
> active link reporting:
>
>                 LnkCap: Port #247, Speed 2.5GT/s, Width x1, ASPM L1, Exit Latency L1 <4us
>                         ClockPM- Surprise- LLActRep+ BwNot- ASPMOptComp+
>
> So when the link goes back to L0 (D3 -> D0 transition) the kernel should
> issue the 100+ ms reset delay in pci_bridge_wait_for_secondary_bus():

This was actually the first thing I tried but it doesn't work. Even a
5 seconds delay doesn't work either.

>
>   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/pci.c#n5045
>
> can you check if that is happening? It should show up in the dmesg when
> CONFIG_PCI_DEBUG=y but I don't see it in yours.

That's because there isn't any child device yet, so the function bails early:
if (!dev->subordinate || list_empty(&dev->subordinate->devices))

Kai-Heng