On Thu, Oct 08, 2015 at 01:32:04PM +0800, Jiang Liu wrote:
> On 2015/10/7 1:47, Bjorn Helgaas wrote:
> >> +struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
> >> + struct acpi_pci_root_ops *ops,
> >> + struct acpi_pci_root_info *info,
> >> + void *sysdata)
> >> +{
> >> + int ret, busnum = root->secondary.start;
> >> + struct acpi_device *device = root->device;
> >> + int node = acpi_get_node(device->handle);
> >> + struct pci_bus *bus;
> >> +
> >> + info->root = root;
> >> + info->bridge = device;
> >> + info->ops = ops;
> >> + INIT_LIST_HEAD(&info->resources);
> >> + snprintf(info->name, sizeof(info->name), "PCI Bus %04x:%02x",
> >> + root->segment, busnum);
> >> +
> >> + if (ops->init_info && ops->init_info(info))
> >> + goto out_release_info;
> >> + ret = acpi_pci_probe_root_resources(info);
> >> + if (ops->prepare_resources)
> >> + ret = ops->prepare_resources(info, ret);
> >> + if (ret < 0)
> >> + goto out_release_info;
> >> + else if (ret > 0)
> >> + pci_acpi_root_add_resources(info);
> >
> > This is unnecessarily complicated: you set "ret", then overwrite it if
> > ops->prepare_resources. By the time you test "ret", it's messy to
> > figure out what it means.
> >
> > Both ops->prepare_resources() and pci_acpi_root_add_resources()
> > should be able to deal with empty resource lists, so can you do the
> > following instead?
> >
> > ret = acpi_pci_probe_root_resources(info);
> > if (ret < 0)
> > goto out_release_info;
>
> The original code is used to handle a special case for x86,
> where acpi_pci_probe_root_resources() fails but ops->prepare_resources()
> succeeds. For x86, PCI host bridge resources may probed by means
> other than ACPI when pci_use_crs is true (AMD and Broadcom hostbridges).
> So we can't return failure when acpi_pci_probe_root_resources() fails.
That's even worse than I thought. I take back my ack; I think this
really needs to be restructured so it does the right thing *and* reads
clearly. Having convoluted generic code to deal with an arch-specific
special case is a recipe for breakage in the future.
Maybe you can move the non-ACPI resource probing from
prepare_resources() into acpi_pci_probe_root_resources() (you could
rename it to something more generic if that helps).
> + ret = acpi_pci_probe_root_resources(info);
> + if (ops->prepare_resources)
> + ret = ops->prepare_resources(info, ret);
> + if (ret < 0)
> + goto out_release_info;
>
> > if (ops->prepare_resources) {
> > ret = ops->prepare_resources(info, ret);
> > if (ret < 0)
> > goto out_release_info;
> > }
> > pci_acpi_root_add_resources(info);
> I will remove the redundant check of (ret > 0) in:
> + else if (ret > 0)
> + pci_acpi_root_add_resources(info);
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