Subject: Re: [PATCH] powerpc/pci: Reuse PHB number on pci_controller add if available

From: Benjamin Herrenschmidt <[email-masked]>
Date: Fri, 11 Mar 2016 08:34:58 +1100

On Thu, 2016-03-10 at 15:11 -0300, Guilherme G. Piccoli wrote:
> The domain/PHB field of PCI addresses has its value obtained from a
> global variable, incremented each time a new domain (represented by
> struct pci_controller) is added on the system. The domain addition
> process happens during boot or due to PCI device hotplug.

I'd rather we use a fixed numbering for domains, for example, under
OPAL, use the opal-id, under phyp, there is also a number in the DT we
can use (forgot what it's called) etc...

> As recent kernels are using predictable naming for network
> interfaces,
> the network stack is more tied to PCI naming. This can be a problem
> in
> hotplug scenarios, because PCI addresses will change if a device is
> removed and then re-added. This situation seems unusual, but it can
> happen if a user wants to replace a NIC without rebooting the
> machine,
> for example.
> 
> This patch changes the way PCI domain values are generated: the
> global
> variable is no longer used; instead, a list is introduced, containing
> a flag that indicates whenever a domain is in use or was released,
> for
> example by a PCI hotplug remove. If the new PHB being added finds a
> free domain, it will use its number; otherwise a new number is
> generated incrementing the higher domain value present on the system.
> No functional changes were introduced.
> 
> Signed-off-by: Guilherme G. Piccoli <[email-masked]>
> ---
>  arch/powerpc/kernel/pci-common.c | 47
> +++++++++++++++++++++++++++++++++++++---
>  1 file changed, 44 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/pci-common.c
> b/arch/powerpc/kernel/pci-common.c
> index 0f7a60f..6eac0dd 100644
> --- a/arch/powerpc/kernel/pci-common.c
> +++ b/arch/powerpc/kernel/pci-common.c
> @@ -44,8 +44,12 @@
>  static DEFINE_SPINLOCK(hose_spinlock);
>  LIST_HEAD(hose_list);
>  
> -/* XXX kill that some day ... */
> -static int global_phb_number;		/* Global phb counter
> */
> +/* Global PHB counter list */
> +struct global_phb_number {
> +	bool used;
> +	struct list_head node;
> +};
> +LIST_HEAD(global_phb_number_list);
>  
>  /* ISA Memory physical address */
>  resource_size_t isa_mem_base;
> @@ -64,6 +68,42 @@ struct dma_map_ops *get_pci_dma_ops(void)
>  }
>  EXPORT_SYMBOL(get_pci_dma_ops);
>  
> +static int get_phb_number(void)
> +{
> +	struct global_phb_number *ptr;
> +	int latest_number = 0;
> +
> +	list_for_each_entry(ptr, &global_phb_number_list, node) {
> +		if (!ptr->used) {
> +			ptr->used = true;
> +			return latest_number;
> +		}
> +		latest_number++;
> +	}
> +
> +	ptr = zalloc_maybe_bootmem(sizeof(struct global_phb_number),
> GFP_KERNEL);
> +	BUG_ON(ptr == NULL);
> +
> +	ptr->used = true;
> +	list_add_tail(&ptr->node, &global_phb_number_list);
> +
> +	return latest_number;
> +}
> +
> +static void release_phb_number(int phb_number)
> +{
> +	struct global_phb_number *ptr;
> +	int current_number = 0;
> +
> +	list_for_each_entry(ptr, &global_phb_number_list, node) {
> +		if (current_number == phb_number) {
> +			ptr->used = false;
> +			return;
> +		}
> +		current_number++;
> +	}
> +}
> +
>  struct pci_controller *pcibios_alloc_controller(struct device_node
> *dev)
>  {
>  	struct pci_controller *phb;
> @@ -72,7 +112,7 @@ struct pci_controller
> *pcibios_alloc_controller(struct device_node *dev)
>  	if (phb == NULL)
>  		return NULL;
>  	spin_lock(&hose_spinlock);
> -	phb->global_number = global_phb_number++;
> +	phb->global_number = get_phb_number();
>  	list_add_tail(&phb->list_node, &hose_list);
>  	spin_unlock(&hose_spinlock);
>  	phb->dn = dev;
> @@ -94,6 +134,7 @@ EXPORT_SYMBOL_GPL(pcibios_alloc_controller);
>  void pcibios_free_controller(struct pci_controller *phb)
>  {
>  	spin_lock(&hose_spinlock);
> +	release_phb_number(phb->global_number);
>  	list_del(&phb->list_node);
>  	spin_unlock(&hose_spinlock);
>