linux-kernel - Re: [Patch v2 2/2] thunderbolt: Teardown tunnels and reset downstream ports created by boot firmware

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Date:   Wed, 13 Dec 2023 08:23:06 +0200
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Sanath S <Sanath.S@....com>
Cc:     mario.limonciello@....com, andreas.noever@...il.com,
        michael.jamet@...el.com, YehezkelShB@...il.com,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Patch v2 2/2] thunderbolt: Teardown tunnels and reset
 downstream ports created by boot firmware

On Wed, Dec 13, 2023 at 08:18:06AM +0200, Mika Westerberg wrote:
> On Wed, Dec 13, 2023 at 07:49:14AM +0200, Mika Westerberg wrote:
> > On Wed, Dec 13, 2023 at 12:46:35AM +0530, Sanath S wrote:
> > > Boot firmware might have created tunnels of its own. Since we cannot
> > > be sure they are usable for us. Tear them down and reset the ports
> > > to handle it as a new hotplug for USB3 routers.
> > > 
> > > Suggested-by: Mario Limonciello <mario.limonciello@....com>
> > > Signed-off-by: Sanath S <Sanath.S@....com>
> > > ---
> > >  drivers/thunderbolt/tb.c | 11 +++++++++++
> > >  1 file changed, 11 insertions(+)
> > > 
> > > diff --git a/drivers/thunderbolt/tb.c b/drivers/thunderbolt/tb.c
> > > index fd49f86e0353..febd0b6972e3 100644
> > > --- a/drivers/thunderbolt/tb.c
> > > +++ b/drivers/thunderbolt/tb.c
> > > @@ -2598,6 +2598,17 @@ static int tb_start(struct tb *tb)
> > >  	tb_switch_tmu_enable(tb->root_switch);
> > >  	/* Full scan to discover devices added before the driver was loaded. */
> > >  	tb_scan_switch(tb->root_switch);
> > > +	/*
> > > +	 * Boot firmware might have created tunnels of its own. Since we cannot
> > > +	 * be sure they are usable for us, Tear them down and reset the ports
> > > +	 * to handle it as new hotplug for USB4 routers.
> > > +	 */
> > > +	if (tb_switch_is_usb4(tb->root_switch)) {
> > > +		tb_switch_discover_tunnels(tb->root_switch,
> > > +					   &tcm->tunnel_list, false);
> > 
> > Why this is needed?
> > 
> > It should be enough, to do simply something like this:
> > 
> > 	if (tb_switch_is_usb4(tb->root_switch))
> > 		tb_switch_reset(tb->root_switch);
> 
> Actually this needs to be done only for USB4 v1 routers since we already
> reset USB4 v2 hosts so something like:
> 
> 	/*
> 	 * Reset USB4 v1 host router to get rid of possible tunnels the
> 	 * boot firmware created. This makes sure all the tunnels are
> 	 * created by us and thus have known configuration.
> 	 *
> 	 * For USB4 v2 and beyond we do this in nhi_reset() using the
> 	 * host router reset interface.
> 	 */
> 	if (usb4_switch_version(tb->root_switch) == 1)
> 		tb_switch_reset(tb->root_switch);
> 
> (possibly add similar comment to the nhi_reset() to refer this one).

Oh, and would it be possible to tie this with the "host_reset" parameter
too somehow? I guess it could be moved to "tb.c" and "tb.h" and then
check it from nhi.c as already done and then here so this would become:

 	if (host_reset && usb4_switch_version(tb->root_switch) == 1)
 		tb_switch_reset(tb->root_switch);

With the idea that the user has a "chicken bit" to disable this
behaviour (and consistent one with USB4 v2). Feel free to make it look
nicer though.