linux-kernel - Re: [PATCH v5 3/8] PCI: Don't block runtime PM for Thunderbolt host hotplug ports

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Date:   Mon, 16 Jan 2017 12:29:27 +0200
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Andreas Noever <andreas.noever@...il.com>,
        linux-pci@...r.kernel.org, linux-pm@...r.kernel.org,
        Bjorn Helgaas <helgaas@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH v5 3/8] PCI: Don't block runtime PM for Thunderbolt host
 hotplug ports

On Sun, Jan 15, 2017 at 09:03:45PM +0100, Lukas Wunner wrote:
> Hotplug ports generally block their parents from suspending to D3hot as
> otherwise their interrupts couldn't be delivered.
> 
> An exception are Thunderbolt host controllers:  They have a separate
> GPIO pin to side-band signal plug events even if the controller is
> powered down or its parent ports are suspended to D3.  They can be told
> apart from Thunderbolt controllers in attached devices by checking if
> they're situated below a non-Thunderbolt device (typically a root port,
> or the downstream port of a PCIe switch in the case of the MacPro6,1).
> 
> To enable runtime PM for Thunderbolt on the Mac, the downstream bridges
> of a host controller must not block runtime PM on the upstream bridge as
> power to the chip is only cut once the upstream bridge has suspended.
> Amend the condition in pci_dev_check_d3cold() accordingly.
> 
> This change does not impact non-Macs as their Thunderbolt hotplug ports
> are handled by the firmware rather than natively by the OS:  The hotplug
> ports are not allowed to suspend in pci_bridge_d3_possible() and keep
> their parent ports awake all the time.  Consequently it is meaningless
> whether they block runtime PM on their parent ports or not.
> 
> Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>

Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>