Re: [PATCH v8 6/9] pci: Introduce a domain number for pci_host_bridge.

[Bjorn Helgaas <bhelgaas@google.com>]

On Tue, Jul 01, 2014 at 07:43:31PM +0100, Liviu Dudau wrote:
> Make it easier to discover the domain number of a bus by storing
> the number in pci_host_bridge for the root bus. Several architectures
> have their own way of storing this information, so it makes sense
> to try to unify the code. While at this, add a new function that
> creates a root bus in a given domain and make pci_create_root_bus()
> a wrapper around this function.

"While at this" is always a good clue that maybe something should be
split into a separate patch :)  This is a very good example, since it
adds a new interface that deserves its own changelog.

> Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
> Tested-by: Tanmay Inamdar <tinamdar@apm.com>
> ---
>  drivers/pci/probe.c | 41 +++++++++++++++++++++++++++++++++--------
>  include/linux/pci.h |  4 ++++
>  2 files changed, 37 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 2c92662..abf5e82 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1748,8 +1748,9 @@ void __weak pcibios_remove_bus(struct pci_bus *bus)
>  {
>  }
>  
> -struct pci_bus *pci_create_root_bus(struct device *parent, int bus,
> -		struct pci_ops *ops, void *sysdata, struct list_head *resources)
> +struct pci_bus *pci_create_root_bus_in_domain(struct device *parent,
> +		int domain, int bus, struct pci_ops *ops, void *sysdata,
> +		struct list_head *resources)

I don't think we should do it this way; this makes it possible to have a
host bridge where "bridge->domain_nr != pci_domain_nr(bridge->bus)".

I wonder if it would help to make a weak pci_domain_nr() function that
returns "bridge->domain_nr".  Then each arch could individually drop its
pci_domain_nr() definition as it was converted, e.g., something like this:

  - Convert every arch pci_domain_nr() from a #define to a non-inline
    function
  - Add bridge.domain_nr, initialized from pci_domain_nr()
  - Add a weak generic pci_domain_nr() that returns bridge.domain_nr
  - Add a way to create a host bridge in a specified domain, so we can
    initialize bridge.domain_nr without using pci_domain_nr()
  - Convert each arch to use the new creation mechanism and drop its
    pci_domain_nr() implementation

>  {
>  	int error;
>  	struct pci_host_bridge *bridge;
> @@ -1762,27 +1763,31 @@ struct pci_bus *pci_create_root_bus(struct device *parent, int bus,
>  
>  	bridge = pci_alloc_host_bridge();
>  	if (!bridge)
> -		return NULL;
> +		return ERR_PTR(-ENOMEM);
>  
>  	bridge->dev.parent = parent;
>  	bridge->dev.release = pci_release_host_bridge_dev;
> +	bridge->domain_nr = domain;
>  
>  	b = pci_alloc_bus();
> -	if (!b)
> +	if (!b) {
> +		error = -ENOMEM;
>  		goto err_out;
> +	}
>  
>  	b->sysdata = sysdata;
>  	b->ops = ops;
>  	b->number = b->busn_res.start = bus;
> -	b2 = pci_find_bus(pci_domain_nr(b), bus);
> +	b2 = pci_find_bus(bridge->domain_nr, bus);
>  	if (b2) {
>  		/* If we already got to this bus through a different bridge, ignore it */
>  		dev_dbg(&b2->dev, "bus already known\n");
> +		error = -EEXIST;
>  		goto err_bus_out;
>  	}
>  
>  	bridge->bus = b;
> -	dev_set_name(&bridge->dev, "pci%04x:%02x", pci_domain_nr(b), bus);
> +	dev_set_name(&bridge->dev, "pci%04x:%02x", bridge->domain_nr, bus);
>  	error = pcibios_root_bridge_prepare(bridge);
>  	if (error)
>  		goto err_out;
> @@ -1801,7 +1806,7 @@ struct pci_bus *pci_create_root_bus(struct device *parent, int bus,
>  
>  	b->dev.class = &pcibus_class;
>  	b->dev.parent = b->bridge;
> -	dev_set_name(&b->dev, "%04x:%02x", pci_domain_nr(b), bus);
> +	dev_set_name(&b->dev, "%04x:%02x", bridge->domain_nr, bus);
>  	error = device_register(&b->dev);
>  	if (error)
>  		goto class_dev_reg_err;
> @@ -1851,7 +1856,27 @@ err_bus_out:
>  	kfree(b);
>  err_out:
>  	kfree(bridge);
> -	return NULL;
> +	return ERR_PTR(error);
> +}
> +
> +struct pci_bus *pci_create_root_bus(struct device *parent, int bus,
> +		struct pci_ops *ops, void *sysdata, struct list_head *resources)
> +{
> +	int domain_nr;
> +	struct pci_bus *b = pci_alloc_bus();
> +	if (!b)
> +		return NULL;
> +
> +	b->sysdata = sysdata;
> +	domain_nr = pci_domain_nr(b);
> +	kfree(b);
> +
> +	b = pci_create_root_bus_in_domain(parent, domain_nr, bus,
> +				ops, sysdata, resources);
> +	if (IS_ERR(b))
> +		return NULL;
> +
> +	return b;
>  }
>  
>  int pci_bus_insert_busn_res(struct pci_bus *b, int bus, int bus_max)
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 466bcd1..7e7b939 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -401,6 +401,7 @@ struct pci_host_bridge_window {
>  struct pci_host_bridge {
>  	struct device dev;
>  	struct pci_bus *bus;		/* root bus */
> +	int domain_nr;
>  	struct list_head windows;	/* pci_host_bridge_windows */
>  	void (*release_fn)(struct pci_host_bridge *);
>  	void *release_data;
> @@ -769,6 +770,9 @@ struct pci_bus *pci_scan_bus(int bus, struct pci_ops *ops, void *sysdata);
>  struct pci_bus *pci_create_root_bus(struct device *parent, int bus,
>  				    struct pci_ops *ops, void *sysdata,
>  				    struct list_head *resources);
> +struct pci_bus *pci_create_root_bus_in_domain(struct device *parent,
> +			int domain, int bus, struct pci_ops *ops,
> +			void *sysdata, struct list_head *resources);
>  int pci_bus_insert_busn_res(struct pci_bus *b, int bus, int busmax);
>  int pci_bus_update_busn_res_end(struct pci_bus *b, int busmax);
>  void pci_bus_release_busn_res(struct pci_bus *b);
> -- 
> 2.0.0
>