On Fri, Apr 20, 2018 at 08:08:23AM -0500, Rob Herring wrote:
> Having a 'bus-range' property for PCI bridges should not be required,
> so remove the warning when missing. There was some confusion with the
> Linux kernel printing a message that no property is present and the OS
> assigned the bus number. This message was intended to be informational
> rather than a warning.
>
> When the firmware doesn't enumerate the PCI bus and leaves it up to the
> OS to do, then it is perfectly fine for the OS to assign bus numbers
> and bus-range is not necessary.
>
> There are a few cases where bus-range is needed or useful as Arnd
> Bergmann summarized:
>
> - Traditionally Linux avoided using multiple PCI domains, but instead
> configured separate PCI host bridges to have non-overlapping
> bus ranges so we can present them to user space as a single
> domain, and run the kernel without CONFIG_PCI_DOMAINS.
> Specifying the bus ranges this way would and give stable bus
> numbers across boots when the probe order is not fixed.
>
> - On certain ARM64 systems, we must only use the first
> 128 bus numbers based on the way the IOMMU identifies
> the device with truncated bus/dev/fn number. There are probably
> others like this, with various limitations.
>
> - To leave some room for hotplugged devices, each slot on
> a host bridge can in theory get a range of bus numbers
> that are available when assigning bus numbers at boot time
>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Signed-off-by: Rob Herring <robh@xxxxxxxxxx>
Merged, thanks.
> ---
> v2:
> - expand the commit message about when bus-range is used or not
>
> checks.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/checks.c b/checks.c
> index 1e6a88c81a99..261c57557ad2 100644
> --- a/checks.c
> +++ b/checks.c
> @@ -792,10 +792,9 @@ static void check_pci_bridge(struct check *c, struct dt_info *dti, struct node *
> FAIL(c, dti, node, "incorrect #size-cells for PCI bridge");
>
> prop = get_property(node, "bus-range");
> - if (!prop) {
> - FAIL(c, dti, node, "missing bus-range for PCI bridge");
> + if (!prop)
> return;
> - }
> +
> if (prop->val.len != (sizeof(cell_t) * 2)) {
> FAIL_PROP(c, dti, node, prop, "value must be 2 cells");
> return;
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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