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

On Wed, Dec 1, 2021 at 8:47 AM Mika Westerberg
[off-list ref] wrote:

Hi,

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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.

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Is this because the FW might not support the same set of functionality?

Yes, that too.

OK

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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!