On Mo, 2024-10-28 at 13:42 +1100, David Gibson wrote: > On Fri, Oct 25, 2024 at 06:13:07PM +0200, Philipp Zabel wrote: > > Do not fail the unnecessary #address-cells/#size-cells check if any > > children of the node have a "ranges" property. > > I think this is correct, but I had to think abuot it for a while, > because it's subtler than it looks. > > If there is no 'ranges' in the node itself, then the child devices' > address space is not mapped into the parent bus. Of course, you can > still establish a local address space for them that (e.g.) could be > accessed indirectly via registers in this bridge device. > > Having a child device which acts as a bridge from this local address > to another subordinate address space, but no children with any > registers directly on the local bus seems odd... but it is logically > possible. > > Given the subtlety, it would be pretty nice to add an explanatory > comment about what this is check for and what some of the edge cases > are. Thank you. Can I steal your wording and add the following comment inside the for_each_child() loop: /* * Even if the child devices' address space is not mapped into * the parent bus (no 'ranges' property on node), children can * still have registers on a local bus, or map local addresses * to another subordinate address space. The properties on the * child nodes then make #address-cells/#size-cells necessary: */ The specific reason for this patch is a PCI device tree overlay [1] where the '#address-cells'/'#size-cells' properties are on the __overlay__ node and a child simple-bus node contains the 'ranges' property mapping between BAR space and the local bus. [1] https://lore.kernel.org/all/20241014124636.24221-2-herve.codina@xxxxxxxxxxx/ > > Suggested-by: Rob Herring <robh@xxxxxxxxxx> > > Link: https://lore.kernel.org/all/CAL_JsqKebRL454poAYZ9i=sCsHqGzmocLy0psQcng-79UWJB-A@xxxxxxxxxxxxxx/ > > Signed-off-by: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx> > > --- > > checks.c | 10 +++------- > > 1 file changed, 3 insertions(+), 7 deletions(-) > > > > diff --git a/checks.c b/checks.c > > index 6e06aeab5503..76fdee2ed030 100644 > > --- a/checks.c > > +++ b/checks.c > > @@ -1217,9 +1217,7 @@ WARNING(avoid_default_addr_size, check_avoid_default_addr_size, NULL, > > static void check_avoid_unnecessary_addr_size(struct check *c, struct dt_info *dti, > > struct node *node) > > { > > - struct property *prop; > > struct node *child; > > - bool has_reg = false; > > > > if (!node->parent || node->addr_cells < 0 || node->size_cells < 0) > > return; > > @@ -1228,13 +1226,11 @@ static void check_avoid_unnecessary_addr_size(struct check *c, struct dt_info *d > > return; > > > > for_each_child(node, child) { > > - prop = get_property(child, "reg"); > > - if (prop) > > - has_reg = true; > > + if (get_property(child, "reg") || get_property(child, "ranges")) > > + return; > > } > > > > - if (!has_reg) > > - FAIL(c, dti, node, "unnecessary #address-cells/#size-cells without \"ranges\", \"dma-ranges\" or child \"reg\" property"); > > + FAIL(c, dti, node, "unnecessary #address-cells/#size-cells without \"ranges\", \"dma-ranges\" or child \"reg\" property"); > > ..also this message needs updating to reference child "ranges" as well. I'll change it to: "unnecessary #address-cells/#size-cells without \"ranges\", \"dma-ranges\" or child \"reg\" or \"ranges\" property" regards Philipp
