Re: [PATCH 0/4] Add device links between tunneled USB3 devices and USB4 Host

[Mika Westerberg <mika.westerberg@linux.intel.com>]

Hi Mario,

On Thu, Jun 20, 2024 at 01:36:56PM -0500, Mario Limonciello wrote:
> On 6/20/2024 01:41, Mika Westerberg wrote:
> > +CC Mario from AMD side to check that we are good and don't break
> > anything accidentally.
> > 
> > On Wed, Jun 19, 2024 at 04:03:01PM +0300, Mathias Nyman wrote:
> > > The relationship between a USB4 Host Interface providing USB3 tunnels,
> > > and tunneled USB3 devices is not represented in device hierarchy.
> > > 
> > > This caused issues with power managment as devices may suspend and
> > > resume in incorrect order.
> > > A device link between the USB4 Host Interface and the USB3 xHCI was
> > > originally added to solve this, preventing the USB4 Host Interface from
> > > suspending if the USB3 xHCI Host was still active.
> > > This unfortunately also prevents USB4 Host Interface from suspending even
> > > if the USB3 xHCI Host is only serving native non-tunneled USB devices.
> > > 
> > > Improve the current powermanagement situation by creating device links
> > > directly from tunneled USB3 devices to the USB4 Host Interface they depend
> > > on instead of a device link between the hosts.
> > > This way USB4 host may suspend when the last tunneled device is
> > > disconnected.
> > > 
> > > Intel xHCI hosts are capable of reporting if connected USB3 devices are
> > > tunneled via vendor specific capabilities.
> > > Use this until a standard way is available.
> > > 
> > > Mathias Nyman (4):
> > >    xhci: Add USB4 tunnel detection for USB3 devices on Intel hosts
> > >    usb: Add tunneled parameter to usb device structure
> > >    usb: acpi: add device link between tunneled USB3 device and USB4 Host
> > >      Interface
> > >    thunderbolt: Don't create device link from USB4 Host Interface to USB3
> > >      xHC host
> > > 
> > >   drivers/thunderbolt/acpi.c       | 40 ++++++------------------
> > >   drivers/usb/core/usb-acpi.c      | 52 ++++++++++++++++++++++++++++++++
> > >   drivers/usb/host/xhci-ext-caps.h |  5 +++
> > >   drivers/usb/host/xhci-hub.c      | 29 ++++++++++++++++++
> > >   drivers/usb/host/xhci.c          | 12 ++++++++
> > >   drivers/usb/host/xhci.h          |  1 +
> > >   include/linux/usb.h              |  2 ++
> > >   7 files changed, 111 insertions(+), 30 deletions(-)
> > > 
> > > -- 
> > > 2.25.1
> 
> Hi Mika,
> 
> Thanks for looping me in.  Unfortunately with this is appears the XHCI
> controller link never gets created.  I've not checked functional impact from
> this, but I'd guess there "should" be some functional problems too.

Thanks for checking!

I think the code that sets up the device link based on ->tunneled should
do that always if the hardware cannot tell if this is native or tunneled
link to keep the existing functionality and only do the "optimization"
if the hardware is capable of identifying that.

Perhaps it can be a callback provided by the xHCI controller driver
(->is_tunneled()) that then defaults to true if the
"usb4-host-interface" property is there and in case of Intel hardware
also checks the proprietary register?