Subject: Re: [PATCH v5] powerpc/pci: Assign fixed PHB number based on device-tree properties

From: Bjorn Helgaas <[email-masked]>
Date: Mon, 2 May 2016 11:57:39 -0500

On Thu, Apr 14, 2016 at 06:55:24PM -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.
> 
> 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 devices are
> 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: now, we use
> device-tree properties to assign fixed PHB numbers to PCI addresses
> when available (meaning pSeries and PowerNV cases). We also use a bitmap
> to allow dynamic PHB numbering when device-tree properties are not
> used. This bitmap keeps track of used PHB numbers and if a PHB is
> released (by hotplug operations for example), it allows the reuse of
> this PHB number, avoiding PCI address to change in case of device remove
> and re-add soon after. No functional changes were introduced.
> 
> Reviewed-by: Gavin Shan <[email-masked]>
> Signed-off-by: Guilherme G. Piccoli <[email-masked]>

I assume the powerpc guys will take care of this.  Let me know if you
need me to do anything.

> ---
>  arch/powerpc/kernel/pci-common.c | 66 ++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 63 insertions(+), 3 deletions(-)
> 
> v5:
>   * Improved comments.
> 
>   * Changed the the Fixed PHB Numbering to set the PHB number bit
>   on the bitmap anyway, avoiding issues when system has virtual PHBs.
> 
>   * Changed the device-tree check order - now, firstly we check for
>   "ibm,opal-phbid" and if it's not available, we try the pSeries case.
> 
> v4:
>   * Minor change (if/else nesting rearranged).
> 
> v3:
>   * Made the bitmap static.
> 
>   * Rearranged if/else statements of Fixed PHB checking.
> 
>   * Improved bitmap checkings, by removing loop and using instead the
>   find_first_zero_bit() function.
> 
>   * Removed the single-statement function release_phb_number() by
>   adding its logic directly into pcibios_free_controller().
> 
>   *Added check for bitmap size before clearing bit, avoiding memory
>   corruption.
> 
> v2:
>   * Added the Fixed PHB Numbering mechanism based on device-tree
>   properties.
> 
>   * Changed list approach to bitmap on the Dynamic PHB Numbering
>   mechanism.
> 
> diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
> index 0f7a60f..ad423c1 100644
> --- a/arch/powerpc/kernel/pci-common.c
> +++ b/arch/powerpc/kernel/pci-common.c
> @@ -41,11 +41,17 @@
>  #include <asm/ppc-pci.h>
>  #include <asm/eeh.h>
>  
> +/* hose_spinlock protects accesses to the the phb_bitmap. */
>  static DEFINE_SPINLOCK(hose_spinlock);
>  LIST_HEAD(hose_list);
>  
> -/* XXX kill that some day ... */
> -static int global_phb_number;		/* Global phb counter */
> +/* For dynamic PHB numbering on get_phb_number(): max number of PHBs. */
> +#define	MAX_PHBS	8192
> +
> +/* For dynamic PHB numbering: used/free PHBs tracking bitmap.
> + * Accesses to this bitmap should be protected by hose_spinlock.
> + */
> +static DECLARE_BITMAP(phb_bitmap, MAX_PHBS);
>  
>  /* ISA Memory physical address */
>  resource_size_t isa_mem_base;
> @@ -64,6 +70,55 @@ struct dma_map_ops *get_pci_dma_ops(void)
>  }
>  EXPORT_SYMBOL(get_pci_dma_ops);
>  
> +/* get_phb_number() function should run under locking
> + * protection, specifically hose_spinlock.
> + */
> +static int get_phb_number(struct device_node *dn)
> +{
> +	const __be64 *prop64;
> +	const __be32 *regs;
> +	int phb_id = 0;
> +
> +	/* Try fixed PHB numbering first, by checking archs and reading
> +	 * the respective device-tree properties. Firstly, try PowerNV by
> +	 * reading "ibm,opal-phbid", only present in OPAL environment.
> +	 */
> +	prop64 = of_get_property(dn, "ibm,opal-phbid", NULL);
> +	if (prop64) {
> +		phb_id = (int)(be64_to_cpup(prop64) & 0xFFFF);
> +
> +	} else if (machine_is(pseries)) {
> +		regs = of_get_property(dn, "reg", NULL);
> +		if (regs)
> +			phb_id = (int)(be32_to_cpu(regs[1]) & 0xFFFF);
> +	} else {
> +		goto dynamic_phb_numbering;
> +	}
> +
> +	/* If we have a huge PHB number obtained from device-tree, no need
> +	 * to worry with the bitmap. Otherwise, we need to be sure we're
> +	 * not trying to use the same PHB number twice.
> +	 */
> +	if (phb_id < MAX_PHBS) {
> +		if (test_bit(phb_id, phb_bitmap))
> +			goto dynamic_phb_numbering;
> +		set_bit(phb_id, phb_bitmap);
> +	}
> +
> +	return phb_id;
> +
> +	/* If not pSeries nor PowerNV, or if fixed PHB numbering tried to add
> +	 * the same PHB number twice, then fallback to dynamic PHB numbering.
> +	 */
> +dynamic_phb_numbering:
> +
> +	phb_id = find_first_zero_bit(phb_bitmap, MAX_PHBS);
> +	BUG_ON(phb_id >= MAX_PHBS); /* Reached maximum number of PHBs. */
> +	set_bit(phb_id, phb_bitmap);
> +
> +	return phb_id;
> +}
> +
>  struct pci_controller *pcibios_alloc_controller(struct device_node *dev)
>  {
>  	struct pci_controller *phb;
> @@ -72,7 +127,7 @@ 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(dev);
>  	list_add_tail(&phb->list_node, &hose_list);
>  	spin_unlock(&hose_spinlock);
>  	phb->dn = dev;
> @@ -94,6 +149,11 @@ EXPORT_SYMBOL_GPL(pcibios_alloc_controller);
>  void pcibios_free_controller(struct pci_controller *phb)
>  {
>  	spin_lock(&hose_spinlock);
> +
> +	/* Clear bit of phb_bitmap to allow reuse of this PHB number. */
> +	if (phb->global_number < MAX_PHBS)
> +		clear_bit(phb->global_number, phb_bitmap);
> +
>  	list_del(&phb->list_node);
>  	spin_unlock(&hose_spinlock);
>  
> -- 
> 2.1.0
> 
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