On Wed, Nov 06, 2024 at 02:23:33PM +0100, Philipp Zabel wrote: > On Mi, 2024-11-06 at 10:55 +1100, David Gibson wrote: > > On Mon, Nov 04, 2024 at 02:32:54PM +0100, Philipp Zabel wrote: > > > 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: > > > */ > > > > Sure! > > Done in v2. > > > > 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/ > > > > Hrm... two things strike me as suspicious about that example. > > > > 1) The __overlay__ node is the PCI bus root... which should already > > have #address-cells and #size-cells in the base tree; it's PCI so > > those values are known and standard. > > dtc doesn't know about this when compiling the overlay. > Removing the #address-cells/#size-cells properties from the __overlay__ > node would cause these compiler warnings: > > DTC drivers/misc/lan966x_pci.dtbo > ../drivers/misc/lan966x_pci.dtso:59.5-60.52: Warning (ranges_format): /fragment@0/__overlay__/pci-ep-bus@0:ranges: "ranges" property has invalid length (40 bytes) (parent #address-cells == 2, child #address-cells == 1, #size-cells == 1) > ../drivers/misc/lan966x_pci.dtso:50.17-174.6: Warning (avoid_default_addr_size): /fragment@0/__overlay__/pci-ep-bus@0: Relying on default #address-cells value > ../drivers/misc/lan966x_pci.dtso:50.17-174.6: Warning (avoid_default_addr_size): /fragment@0/__overlay__/pci-ep-bus@0: Relying on default #size-cells value Ah, yeah, I realised that after I sent the mail. That's the hackiness of the overlay design showing itself again. There's a limit to how well the checks can work on an overlay alone - and even when it can theoretically work, not all the checks have been written with that in mind. Duplicating the #address-cells in the overlay is a reasonable workaround under the circumstances, but it's pretty ugly :(. > > 2) The PCI<->simple-bus bridge must surely have at least the normal > > configuration space registers, and so should have a 'reg' property as > > well as 'ranges'. > > This I don't know about. > > > > > > 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" > > Done in v2. > > regards > Philipp > -- David Gibson (he or they) | 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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