linux-kernel - Re: [PATCH] [RFC] thunderbolt: Add delay for Dell U2725QE link width

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Message-ID: <CAFv23QknLmZkC9Fc0FTFKCofngRUQipw4hGVG_P2k+TUb=KOeA@mail.gmail.com>
Date: Thu, 18 Dec 2025 09:38:13 +0800
From: AceLan Kao <acelan.kao@...onical.com>
To: Mario Limonciello <mario.limonciello@....com>
Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>, 
	Andreas Noever <andreas.noever@...il.com>, Mika Westerberg <westeri@...nel.org>, 
	Yehezkel Bernat <YehezkelShB@...il.com>, linux-usb@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Sanath.S@....com, 
	"Lin, Wayne" <Wayne.Lin@....com>
Subject: Re: [PATCH] [RFC] thunderbolt: Add delay for Dell U2725QE link width

Mario Limonciello <mario.limonciello@....com> 於 2025年12月17日週三 下午11:53寫道：
>
> On 12/17/25 6:55 AM, Mika Westerberg wrote:
> > Hi,
> >
> > On Wed, Dec 17, 2025 at 11:06:52AM +0800, AceLan Kao wrote:
> >>>> By default it does not access retimers beyond the Type-C connector. I
> >>>> wonder if you have CONFIG_USB4_DEBUGFS_MARGINING set in your kernel
> >>>> .config? And if yes can you disable that and try again.
> >> Sorry, it looks like I got some troubles with my MTA, some emails are
> >> not sent out correctly.
> >>
> >> I've rebuilt the kernel without CONFIG_USB4_DEBUGFS_MARGINING, and
> >> here is the log
> >> There is a tbt storage daisy-chained after the tbt monitor, it's
> >> easier to reproduce this issue.
> >> https://people.canonical.com/~acelan/bugs/tbt_call_trace/intel/merged_6.18.0-d358e5254674+.2.out
> >>
> >> And this one is only the tbt monitor plugged.
> >> https://people.canonical.com/~acelan/bugs/tbt_call_trace/intel/merged_6.18.0-d358e5254674+.3.out
> >
> > Okay from the first trace at least scanning of the retimer at index 2
> > (which does not exist) does not complete too fast and I suspect there is
> > some timeout on the device side that triggers. We had already similar with
> > Pluggable devices but perhaps this is implemented in the Dell version too?
> >
> > I wonder it is enough if we set configuration valid and then scan the
> > downstream retimers? Can you try the attached patch? We do need to scan
> > them before DP tunnels are created to support ALPM (this is work in
> > progress).
>
> If it needs to go even later - there is OFC the possibility of doing
> upstream ones first and USB3 tunnels first too.
>
> I'd say if the below doesn't work Acelan you can try pushing it right
> before tp_add_dp_resources() to see.
Hi Mario,

It's still no luck to move tb_retimer_scan() right before tp_add_dp_resources()
https://people.canonical.com/~acelan/bugs/tbt_call_trace/intel/merged_6.18.0-d358e5254674+.patched2.out

>
> >
> > diff --git a/drivers/thunderbolt/tb.c b/drivers/thunderbolt/tb.c
> > index d7f32a63fc1e..e23e0ee9c95f 100644
> > --- a/drivers/thunderbolt/tb.c
> > +++ b/drivers/thunderbolt/tb.c
> > @@ -1380,14 +1380,6 @@ static void tb_scan_port(struct tb_port *port)
> >       upstream_port = tb_upstream_port(sw);
> >       tb_configure_link(port, upstream_port, sw);
> >
> > -     /*
> > -      * Scan for downstream retimers. We only scan them after the
> > -      * router has been enumerated to avoid issues with certain
> > -      * Pluggable devices that expect the host to enumerate them
> > -      * within certain timeout.
> > -      */
> > -     tb_retimer_scan(port, true);
> > -
> >       /*
> >        * CL0s and CL1 are enabled and supported together.
> >        * Silently ignore CLx enabling in case CLx is not supported.
> > @@ -1406,6 +1398,13 @@ static void tb_scan_port(struct tb_port *port)
> >        */
> >       tb_switch_configuration_valid(sw);
> >
> > +     /*
> > +      * Scan for downstream retimers. We only scan them after the
> > +      * router has been enumerated to avoid issues with certain
> > +      * Pluggable devices that expect the host to enumerate them
> > +      * within certain timeout.
> > +      */
> > +     tb_retimer_scan(port, true);
Hi Mika,

This doesn't work.
https://people.canonical.com/~acelan/bugs/tbt_call_trace/intel/merged_6.18.0-d358e5254674+.patched1.out

>
> Just a note in case this turns into a proper patch/solution.  Make sure
> you update the comment to cover this monitor too.
>
> >       /* Scan upstream retimers */
> >       tb_retimer_scan(upstream_port, true);
> >