Hi Rob, CC broonie CC somlo On Wed, Feb 21, 2024 at 3:06 PM Rob Herring <robh+dt@xxxxxxxxxx> wrote: > 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> Thanks for your patch, which is now commit 7b937cc243e5b1df ("of: Create of_root if no dtb provided by firmware") in dt-rh/for-next (next-20240312 and later). On my OrangeCrab FPGA running Linux on LiteX/VexRiscv-V, the attached OLED display now fails to probe: -ssd130x-i2c 0-003c: supply vcc not found, using dummy regulator -[drm] Initialized ssd130x 1.0.0 20220131 for 0-003c on minor 0 +ssd130x-i2c 0-003c: incomplete constraints, dummy supplies not allowed +ssd130x-i2c 0-003c: error -ENODEV: Failed to get VCC regulator > > > @@ -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. How many systems in the wild violate this? Apparently the DTS generated by LiteX does not have a root compatible (and model) property, hence of_have_populated_dt() returns false. While my gateware and DTS is quite old, a quick look at recent litex_json2dts_linux.py history shows this is still true for current LiteX. Now, how is this related to the failure I am seeing? drivers/regulator/core.c has: static bool have_full_constraints(void) { return has_full_constraints || of_have_populated_dt(); } and static int __init regulator_init_complete(void) { /* * Since DT doesn't provide an idiomatic mechanism for * enabling full constraints and since it's much more natural * with DT to provide them just assume that a DT enabled * system has full constraints. */ if (of_have_populated_dt()) has_full_constraints = true; ... } late_initcall_sync(regulator_init_complete); (The latter looks a bit futile, as have_full_constraints() already contains a check for of_have_populated_dt()?) When have_full_constraints() returns false, any dummy regulator will fail to probe. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
