Re: [PATCH v3 05/12] PCI: Detect root port of internal USB4 devices by `usb4-host-interface`

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Feb 11, 2022 at 01:32:43PM -0600, Mario Limonciello wrote:
> The root port used for PCIe tunneling should be marked as removable to
> ensure that the entire chain is marked removable.
> 
> This can be done by looking for the device property specified in
> the ACPI tables `usb4-host-interface`.
> 
> Suggested-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> Link: https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports#mapping-native-protocols-pcie-displayport-tunneled-through-usb4-to-usb4-host-routers
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
>  drivers/pci/pci-acpi.c | 10 ++++++++++
>  drivers/pci/pci.h      |  5 +++++
>  drivers/pci/probe.c    |  1 +
>  3 files changed, 16 insertions(+)
> 
> diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> index a42dbf448860..6368e5633b1b 100644
> --- a/drivers/pci/pci-acpi.c
> +++ b/drivers/pci/pci-acpi.c
> @@ -1391,6 +1391,16 @@ void pci_acpi_cleanup(struct device *dev, struct acpi_device *adev)
>  	}
>  }
>  
> +bool pci_acpi_is_usb4(struct pci_dev *dev)
> +{
> +	struct acpi_device *adev = ACPI_COMPANION(&dev->dev);
> +
> +	if (!adev)
> +		return false;
> +	return fwnode_property_present(acpi_fwnode_handle(adev),
> +				       "usb4-host-interface");

Maybe it's obvious to everybody but me that "USB4" means this device
is removable.  The Microsoft reference above doesn't say anything
about removability.

My expectation is that "USB" (like "PCI" and "PCIe") tells me
something about how a device is electrically connected and how
software can operate it.  It doesn't really tell me anything about
whether those electrical connections are permanent, made through an
internal slot, or made through an external connector and cable.

> +}
> +
>  static struct fwnode_handle *(*pci_msi_get_fwnode_cb)(struct device *dev);
>  
>  /**
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 3d60cabde1a1..359607c0542d 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -695,6 +695,7 @@ void acpi_pci_refresh_power_state(struct pci_dev *dev);
>  int acpi_pci_wakeup(struct pci_dev *dev, bool enable);
>  bool acpi_pci_need_resume(struct pci_dev *dev);
>  pci_power_t acpi_pci_choose_state(struct pci_dev *pdev);
> +bool pci_acpi_is_usb4(struct pci_dev *dev);
>  #else
>  static inline int pci_dev_acpi_reset(struct pci_dev *dev, bool probe)
>  {
> @@ -734,6 +735,10 @@ static inline pci_power_t acpi_pci_choose_state(struct pci_dev *pdev)
>  {
>  	return PCI_POWER_ERROR;
>  }
> +static inline bool pci_acpi_is_usb4(struct pci_dev *dev)
> +{
> +	return false;
> +}
>  #endif
>  
>  #ifdef CONFIG_PCIEASPM
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index e41656cdd8f0..2693211d31cf 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1610,6 +1610,7 @@ static void pci_set_removable(struct pci_dev *dev)
>  	 * exposed as "removable" to userspace.
>  	 */
>  	if (vsec ||
> +	    pci_acpi_is_usb4(dev) ||
>  	    (parent &&
>  	    (parent->external_facing || dev_is_removable(&parent->dev))))
>  		dev_set_removable(&dev->dev, DEVICE_REMOVABLE);
> -- 
> 2.34.1
>