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 15:26:28 +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

Hi Mika,

On Mon, Sep 5, 2022 at 3:06 PM Mika Westerberg
<mika.westerberg@...ux.intel.com> wrote:
>
> Hi,
>
> On Mon, Sep 05, 2022 at 02:56:22PM +0800, Kai-Heng Feng wrote:
> > AMD USB4 can not detect external PCIe devices like external NVMe when
> > it's hotplugged, because card/link are not up:
> >
> > pcieport 0000:00:04.1: pciehp: pciehp_check_link_active: lnk_status = 1101
>
> I think the correct solution is then to block them from runtime
> suspending entirely.

Do you mean disable runtime suspend completely? Or just block runtime
suspend for a period?

>
> > Use `lspci` to resume pciehp bridges can find external devices.
> >
> > A long delay before checking card/link presence doesn't help, either.
> > The only way to make the hotplug work is to enable pciehp interrupt and
> > check card presence after the TB switch is added.
> >
> > Since the topology of USB4 and its PCIe bridges are siblings, hardcode
> > the bridge ID so TBT driver can wake them up to check presence.
>
> Let's not add PCI things into TBT driver unless absolutely necessary.

OK. It's getting harder as different components are intertwined
together on new hardwares...

>
> At least on Intel hardware the PCIe hotplug is signaled by SCI when the
> root port is in D3, I wonder if AMD has something similar.

Yes those root ports are resumed to D0 when something is plugged. They
however fail to detect any externel PCIe devices.

Kai-Heng