Re: [PATCH v2 08/13] PCI: Allow runtime PM for Thunderbolt hotplug ports on Macs

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, May 13, 2016 at 01:15:31PM +0200, Lukas Wunner wrote:
> Thunderbolt controllers have a pin to signal plug events while the
> controller is powered down.  On Macs this pin is wired to the
> southbridge and causes a GPE to be fired.  The OS may then power up the
> controller to probe the newly connected device.  It is thus okay to let
> Thunderbolt hotplug ports go to D3 on Macs.
> 
> Signed-off-by: Lukas Wunner <lukas@wunner.de>
> ---
>  drivers/pci/pcie/portdrv_pci.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/pcie/portdrv_pci.c b/drivers/pci/pcie/portdrv_pci.c
> index f75d4b5..7860ab3 100644
> --- a/drivers/pci/pcie/portdrv_pci.c
> +++ b/drivers/pci/pcie/portdrv_pci.c
> @@ -224,9 +224,12 @@ static int pcie_portdrv_probe(struct pci_dev *dev,
>  	 * to enumerate devices behind this port properly (the port is
>  	 * powered down preventing all config space accesses to the
>  	 * subordinate devices).  We can't be sure for native PCIe hotplug
> -	 * either so prevent that as well.
> +	 * either so prevent that as well.  However Thunderbolt controllers
> +	 * on Macs are capable of side-band signaling plug events while
> +	 * powered down, so allow them to suspend.
>  	 */
> -	if (!dev->is_hotplug_bridge) {
> +	if (!dev->is_hotplug_bridge ||
> +	    (dev->is_thunderbolt && dmi_match(DMI_SYS_VENDOR, "Apple Inc."))) {

I'd rather have a bit in the pci_dev to control this.  I don't know
how this would be different from the recently-added "bridge_d3" bit.
The bit could be set by a quirk.

It'd be nice if it were a single bit so we don't have to test
is_hotplug_bridge *and* another bit.

>  		/*
>  		 * Keep the port resumed 10ms to make sure things like
>  		 * config space accesses from userspace (lspci) will not
> @@ -243,7 +246,8 @@ static int pcie_portdrv_probe(struct pci_dev *dev,
>  
>  static void pcie_portdrv_remove(struct pci_dev *dev)
>  {
> -	if (!dev->is_hotplug_bridge) {
> +	if (!dev->is_hotplug_bridge ||
> +	    (dev->is_thunderbolt && dmi_match(DMI_SYS_VENDOR, "Apple Inc."))) {
>  		pm_runtime_forbid(&dev->dev);
>  		pm_runtime_get_noresume(&dev->dev);
>  		pm_runtime_dont_use_autosuspend(&dev->dev);
> -- 
> 2.8.1
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-pci" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html