On Mon, Jul 1, 2013 at 9:10 AM, Wei Yang <weiyang@xxxxxxxxxxxxxxxxxx> wrote:
> Normally, on one pci bus there would be more devices than pci buses. When
> calculating the depth of pci bus, it would be more time efficient by
> enumerating through the child buses instead of the child devices.
>
> Also by doing so, the code seems more self explaining. Previously, it go
> through the pci devices and check whether a bridge introduce a child bus or
> not, which needs more background knowledge to understand it.
>
> This patch caculating the depth by enumerating on pci bus hierachy in an
> iterative way.
Your code does have the advantage of not being recursive, but the
original code is significantly shorter and, in my opinion, much more
readable. This is not in a performance path, so I don't see any
advantage in optimizing.
> Signed-off-by: Wei Yang <weiyang@xxxxxxxxxxxxxxxxxx>
> Reviewed-by: Gavin Shan <shangw@xxxxxxxxxxxxxxxxxx>
> Reviewed-by: Ram Pai <linuxram@xxxxxxxxxx>
> Reviewed-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
> Reviewed-by: Mike Qiu <qiudayu@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/pci/setup-bus.c | 43 ++++++++++++++++++++++++++++++++-----------
> 1 files changed, 32 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> index 16abaaa..b333f73 100644
> --- a/drivers/pci/setup-bus.c
> +++ b/drivers/pci/setup-bus.c
> @@ -1299,22 +1299,43 @@ static void pci_bus_dump_resources(struct pci_bus *bus)
>
> static int __init pci_bus_get_depth(struct pci_bus *bus)
> {
> - int depth = 0;
> - struct pci_dev *dev;
> + int max_depth, depth;
> + struct pci_bus *parent, *curr;
> + struct list_head *node;
>
> - list_for_each_entry(dev, &bus->devices, bus_list) {
> - int ret;
> - struct pci_bus *b = dev->subordinate;
> - if (!b)
> - continue;
> + /* no child? */
> + if (list_empty(&bus->children))
> + return 0;
>
> - ret = pci_bus_get_depth(b);
> - if (ret + 1 > depth)
> - depth = ret + 1;
> + node = bus->children.next;
> + parent = bus;
> + max_depth = depth = 1;
> +
> + while (parent) {
> + /* hit the head, go back to parent level */
> + if (node == &parent->children) {
> + node = parent->node.next;
> + parent = parent->parent;
> + depth--;
> + continue;
> + }
> + curr = list_entry(node, struct pci_bus, node);
> + /* depth first */
> + if (!list_empty(&curr->children)) {
> + node = curr->children.next;
> + parent = curr;
> + depth++;
> + if (max_depth < depth)
> + max_depth = depth;
> + }
> + /* no child, go to the sibling */
> + else
> + node = curr->node.next;
> }
>
> - return depth;
> + return max_depth;
> }
> +
> static int __init pci_get_max_depth(void)
> {
> int depth = 0;
> --
> 1.7.5.4
>
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