Hi Rob,
CC broonie CC somlo
On Wed, Feb 21, 2024 at 3:06 PM Rob Herring robh+dt@kernel.org wrote:
On Fri, Feb 16, 2024 at 11:08 PM Saurabh Singh Sengar ssengar@linux.microsoft.com 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@kernel.org: Update of_have_populated_dt() to treat this empty dtb as not populated. Drop setup_of() initcall]
Signed-off-by: Frank Rowand frowand.list@gmail.com Link: https://lore.kernel.org/r/20230317053415.2254616-2-frowand.list@gmail.com Cc: Rob Herring robh+dt@kernel.org Signed-off-by: Stephen Boyd sboyd@kernel.org
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