On Fri, Feb 16, 2024 at 11:08 PM Saurabh Singh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx> wrote: > > On Fri, Feb 16, 2024 at 05:05:51PM -0800, Frank Rowand wrote: > > When enabling CONFIG_OF on a platform where 'of_root' is not populated > > by firmware, we end up without a root node. In order to apply overlays > > and create subnodes of the root node, we need one. Create this root node > > by unflattening an empty builtin dtb. > > > > If firmware provides a flattened device tree (FDT) then the FDT is > > unflattened via setup_arch(). Otherwise, the call to > > unflatten(_and_copy)?_device_tree() will create an empty root node. > > > > We make of_have_populated_dt() return true only if the DTB was loaded by > > firmware so that existing callers don't change behavior after this > > patch. The call in the of platform code is removed because it prevents > > overlays from creating platform devices when the empty root node is > > used. > > > > [sboyd@xxxxxxxxxx: Update of_have_populated_dt() to treat this empty dtb > > as not populated. Drop setup_of() initcall] > > > > Signed-off-by: Frank Rowand <frowand.list@xxxxxxxxx> > > Link: https://lore.kernel.org/r/20230317053415.2254616-2-frowand.list@xxxxxxxxx > > Cc: Rob Herring <robh+dt@xxxxxxxxxx> > > Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxx> > > --- > > @@ -1645,6 +1635,21 @@ static inline bool of_device_is_system_power_controller(const struct device_node > > return of_property_read_bool(np, "system-power-controller"); > > } > > > > +/** > > + * of_have_populated_dt() - Has DT been populated by bootloader > > + * > > + * Return: True if a DTB has been populated by the bootloader and it isn't the > > + * empty builtin one. False otherwise. > > + */ > > +static inline bool of_have_populated_dt(void) > > +{ > > +#ifdef CONFIG_OF > > + return of_property_present(of_root, "compatible"); > > This adds the strict check for compatible which makes compatible > to be mandatory for root nodes. So far, DeviceTree without compatible > property in root nodes can work. Do we want to make this documented > somewhere ? It already is in the DT spec and schemas. Rob
