Date:   Thu, 14 Dec 2023 09:07:46 +0200
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Sanath S <sanaths2@....com>
Cc:     Sanath S <Sanath.S@....com>, 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 Thu, Dec 14, 2023 at 12:08:34PM +0530, Sanath S wrote:
> 
> On 12/13/2023 5:22 PM, Mika Westerberg wrote:
> > On Wed, Dec 13, 2023 at 04:04:57PM +0530, Sanath S wrote:
> > > On 12/13/2023 11:53 AM, Mika Westerberg wrote:
> > > > 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);
> > > If we don't tear down of tunnels before performing the DPR, the PCIe
> > > enumeration is failing.
> > > 
> > > PCIe link is not coming up after DPR. Below log is missing without
> > > performing path
> > > deactivation before performing DPR and hence PCIe enumeration is not
> > > initiated.
> > > 
> > > [  746.630865] pcieport 0000:00:03.1: pciehp: Slot(0-1): Card present
> > > [  746.630885] pcieport 0000:00:03.1: pciehp: Slot(0-1): Link Up
> > > 
> > > I think when we do a DPR, it internally does some handling with PCI Path
> > > Enable bit(PE).
> > > So, deactivation of PCIe path is necessary for DPR to work.
> > Rigth, it should be enough to reset the protocol adapter config and path
> > config spaces. I guess using discovery at this point is fine too but I
> > would at least check how complex doing the minimal "reset" turns out.
> > 
> > I mean in tb_switch_reset() for USB4 v1 routers it can go over all the
> > adapters and perform "cleanup" or so.
> I gave it a thought yesterday and we can do something like this:
> 
> We are already doing tb_discovery(tb) in tb_start. This would
> discover the path configuration done by Boot firmware.
> 
> Now, we can place the tb_switch_reset() right below that api with
> conditions suggested by you.
> 
> And tb_switch_reset() would internally DPR for all down steam ports.
> 
> It can look something like below:
> 
>     /* Find out tunnels created by the boot firmware */
>         tb_discover_tunnels(tb);
>     /*
>      * 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 (host_reset && usb4_switch_version(tb->root_switch) == 1)
>         tb_switch_reset(tb->root_switch);
> 
> With this, we are making sure while we get a unplug event after doing a DPR,
> We are clearing all the paths established by Boot firmware. This wouldn't be
> possible
> if we had not discovered the paths before we perform DPR.
> 
> It would create inconsistency for a new hot plug if we have not cleared the
> path configurations
> of previous hot unplug events.

Right. I would still check if doing protocol adapter "reset" + path
config space clear in tb_switch_reset() is enough and how complex that
ends up to be. I think that's all what is needed.

If it turns out too complex, yes I guess something like this:

	/* Find out tunnels created by the boot firmware */
	tb_discover_tunnels(tb);
	/* Add DP resources from the DP tunnels created by the boot firmware */
	tb_discover_dp_resources(tb);

	if (host_reset && usb4_switch_version(tb->root_switch) == 1) {
		struct tb_tunnel *n, *tunnel;

		list_for_each_entry_safe(tunnel, n, &tcm->tunnel_list, list)
			tb_deactivate_and_free_tunnel(tunnel);

		tb_switch_reset(tb->root_switch);
	}

With proper comments would work, no?

Regarding "host_reset", I think we can actually keep it in nhi.c and add
a parameter to cm_ops->start(reset) that gets passed to the "CM
implementation". Or something along those lines.

> > > > > 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);
> > > Is host_reset necessary for USB4 v1 routers ? I did not use host_reset in
> > > this case.
> > > If its needed, then we have to modify to enable host_reset in nhi.c as well.
> > Well you are effectively doing that here, no? You "reset" the host
> > router therefore tying this to the same command line parameter makes
> > sense and allows user an "escape hatch" if this turns out breaking
> > things.

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