linux-kernel - Re: [RFC 1/3] thunderbolt: Allow XHCI device links to enter runtime pm

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Message-ID: <Yzu+yq07pIfpEbnG@black.fi.intel.com>
Date:   Tue, 4 Oct 2022 08:04:10 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Mario Limonciello <mario.limonciello@....com>
Cc:     "open list:THUNDERBOLT DRIVER" <linux-usb@...r.kernel.org>,
        linux-kernel@...r.kernel.org, Sanju.Mehta@....com
Subject: Re: [RFC 1/3] thunderbolt: Allow XHCI device links to enter runtime
 pm

Hi Mario,

On Mon, Oct 03, 2022 at 11:12:23PM -0500, Mario Limonciello wrote:
> Both on Intel's and AMD's USB4 designs it's important that the device
> link to the XHCI controller used for tunneling is able to go into D3
> for appropriate low power consumption features as well as for system
> suspend states such as s0i3.
> 
> Historically this is accomplished by adding to a hardcoded list in the
> XHCI driver, but this requires a change for every single platform.
> 
> We have a very good proxy that it's safe to do this since the firmware
> has indicated the device link needs to be made.  So opt all XHCI
> controllers with these device links into runtime PM.

This is good idea.

However, it misses the fact that we have FW CM as well in Intel
integrated TBT platforms (ICL, TGL and ADL) and with those you don't
have the device link (I think ADL has it for both, though) so we would
still need to keep the list in xHCI.