Re: [PATCH 2/6] thunderbolt: Tear down existing tunnels when resuming from hibernate

[Yehezkel Bernat <yehezkelshb@gmail.com>]

On Wed, Dec 1, 2021 at 8:47 AM Mika Westerberg
<mika.westerberg@linux.intel.com> wrote:
>
> Hi,
>
> > > > > reason we re-use the tunnel discovery functionality and find out all the
> > > > > existing tunnels, and tear them down. Once that is done we can restore
> > > > > our tunnels.
> > > >
> > > > Hm, what if the system is running from a Thunderbolt-attached drive?
> > > > Will the mount points survive tearing down and re-establishing the
> > > > tunnels to that drive?
> > >
> > > Yes, they should. PCI is waiting for the TBT to resume so it should not
> > > notice this, and all the data is at point still synced out to the disks.
> >
> > But the user will notice the screen flashing, probably?
>
> They will notice flashing anyway because we jump from one kernel to
> another (as this is suspend-to-disk which involves shutting down the
> machine and booting to "fresh" resume kernel first). We actually tear
> down all the DP tunnels before we even enter suspend-to-disk (see
> 81a2e3e49f1f ("thunderbolt: Tear down DP tunnels when suspending")).
>

Ah, thanks.

> > Is this because the FW might not support the same set of functionality?
>
> Yes, that too.

OK

> > Maybe we can continue using the already established tunnels after
> > discovering them?
>
> Yes we could but that would require us to map the existing tunnels with
> the ones we had prior, and also indentify any new tunnels or missing
> ones. This makes it more complex, and the approach here seem to work
> according to my testing :) I can look for that solution too if you think
> it is necessary.

Following the previous points, I don't see any value in trying the
more complex solution.
Thanks!