Re: [PATCH v3 1/2] PCI: add helper function to find root port for device

[Bjorn Helgaas <bhelgaas@google.com>]

On Tue, Jan 13, 2015 at 08:57:27PM +0100, Lucas Stach wrote:
> This adds a simple way to get the root port a given device
> is connected to.
> 
> Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> ---
> v2: new patch in v2
> v3: rename to pci_find_rootport to fit better with other API
> ---
>  drivers/pci/search.c | 20 ++++++++++++++++++++
>  include/linux/pci.h  |  1 +
>  2 files changed, 21 insertions(+)
> 
> diff --git a/drivers/pci/search.c b/drivers/pci/search.c
> index a20ce7d5e2a7..7254f126096d 100644
> --- a/drivers/pci/search.c
> +++ b/drivers/pci/search.c
> @@ -384,3 +384,23 @@ int pci_dev_present(const struct pci_device_id *ids)
>  	return 0;
>  }
>  EXPORT_SYMBOL(pci_dev_present);
> +
> +/**
> + * pci_find_root_port - Returns the root port the given device is connected to.
> + * @dev: PCI device for which the root port should be found.
> + */
> +struct pci_dev *pci_find_root_port(struct pci_dev *dev)

This seems a little too generic.  There are still PCI (non-PCIe) systems,
and on those this will return some non-Root Port device, the meaning of
which is unclear.  I'm happy to put something like this in pci-tegra.c, but
until there are other potential users and we sort out the PCI/PCIe-ness of
the interface, I don't really want to make it global and exported.

> +{
> +	struct pci_bus *bus = dev->bus;
> +
> +	/* If there is no bridge on the bus the passed device is a root port. */

This assumption is false -- see the comment at pci_is_root_bus().

> +	if (!bus->self)
> +		return dev;
> +
> +	/* Walk up the PCI hierarchy to the first level below the root. */
> +	while (bus->parent && bus->parent->self)
> +		bus = bus->parent;
> +
> +	return bus->self;
> +}
> +EXPORT_SYMBOL(pci_find_root_port);
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 360a966a97a5..f4321c5ba653 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -844,6 +844,7 @@ static inline struct pci_dev *pci_get_bus_and_slot(unsigned int bus,
>  }
>  struct pci_dev *pci_get_class(unsigned int class, struct pci_dev *from);
>  int pci_dev_present(const struct pci_device_id *ids);
> +struct pci_dev *pci_find_root_port(struct pci_dev *dev);
>  
>  int pci_bus_read_config_byte(struct pci_bus *bus, unsigned int devfn,
>  			     int where, u8 *val);
> -- 
> 2.1.4
>