Subject: Re: [PATCH 3/6] powerpc/fsl-pci: Determine primary bus by looking for ISA node

From: Scott Wood <[email-masked]>
Date: Tue, 24 Jul 2012 13:47:53 -0500

On 07/24/2012 05:20 AM, Jia Hongtao wrote:
> PCI host bridge is primary bus if it contains an ISA node. But not all boards
> fit this rule. Device tree should be updated for all these boards.
> 
> Signed-off-by: Jia Hongtao <[email-masked]>
> Signed-off-by: Li Yang <[email-masked]>
> ---
>  arch/powerpc/include/asm/pci-bridge.h |    1 +
>  arch/powerpc/sysdev/fsl_pci.c         |   31 ++++++++++++++++++++++++-------
>  arch/powerpc/sysdev/fsl_pci.h         |   12 +++++++++++-
>  3 files changed, 36 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/pci-bridge.h b/arch/powerpc/include/asm/pci-bridge.h
> index ac39e6a..b48fa7f 100644
> --- a/arch/powerpc/include/asm/pci-bridge.h
> +++ b/arch/powerpc/include/asm/pci-bridge.h
> @@ -20,6 +20,7 @@ struct device_node;
>  struct pci_controller {
>  	struct pci_bus *bus;
>  	char is_dynamic;
> +	int is_primary;
>  #ifdef CONFIG_PPC64
>  	int node;
>  #endif
> diff --git a/arch/powerpc/sysdev/fsl_pci.c b/arch/powerpc/sysdev/fsl_pci.c
> index 99a3e78..2a369be 100644
> --- a/arch/powerpc/sysdev/fsl_pci.c
> +++ b/arch/powerpc/sysdev/fsl_pci.c
> @@ -453,6 +453,7 @@ int __init fsl_add_bridge(struct device_node *dev, int is_primary)
>  
>  	hose->first_busno = bus_range ? bus_range[0] : 0x0;
>  	hose->last_busno = bus_range ? bus_range[1] : 0xff;
> +	hose->is_primary = is_primary;
>  
>  	setup_indirect_pci(hose, rsrc.start, rsrc.start + 0x4,
>  		PPC_INDIRECT_TYPE_BIG_ENDIAN);
> @@ -932,18 +933,34 @@ void pci_check_swiotlb(void)
>  }
>  #endif
>  
> -int primary_phb_addr;
> +/*
> + * Recursively scan all the children nodes of parent and find out if there
> + * is "isa" node. Return 1 if parent has isa node otherwise return 0.
> + */
> +int has_isa_node(struct device_node *parent)
> +{
> +	static int result;
> +	struct device_node *cur_child;
> +
> +	cur_child = NULL;
> +	result = 0;
> +	while (!result && (cur_child = of_get_next_child(parent, cur_child))) {
> +		/* Get "isa" node and return 1 */
> +		if (of_node_cmp(cur_child->type, "isa") == 0)
> +			return result = 1;
> +		has_isa_node(cur_child);
> +	}
> +
> +	return result;
> +}

Why are you reimplementing this?  It's already in Linus's tree.  See
fsl_pci_init().

Plus, your version is recursive which is unacceptable in kernel code
with a small stack (outside of a few rare examples where the depth has a
small fixed upper bound), and once it finds an ISA node, it returns 1
forever, regardless of what node you pass in in the future.

-Scott