Quoting Rob Herring (2024-01-15 12:32:30)

On Fri, Jan 12, 2024 at 12:07:47PM -0800, Stephen Boyd wrote:

quoted

diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
index da9826accb1b..9628e48baa15 100644
--- a/drivers/of/Kconfig
+++ b/drivers/of/Kconfig

@@ -54,9 +54,14 @@ config OF_FLATTREE
      select CRC32
 
 config OF_EARLY_FLATTREE
-     bool
+     bool "Functions for accessing Flat Devicetree (FDT) early in boot"

I think we could instead just get rid of this kconfig option. Or 
always enable with CONFIG_OF (except on Sparc). The only cost of 
enabling it is init section functions which get freed anyways.

Getting rid of it is a more massive change. It can be the default and
kept hidden instead? If it can't be selected on Sparc then it should be
hidden there anyway.

quoted

      select DMA_DECLARE_COHERENT if HAS_DMA && HAS_IOMEM
      select OF_FLATTREE
+     help
+       Normally selected by platforms that process an FDT that has been
+       passed to the kernel by the bootloader.  If the bootloader does not
+       pass an FDT to the kernel and you need an empty devicetree that
+       contains only a root node to exist, then say Y here.
 
 config OF_PROMTREE
      bool

[...]

quoted

@@ -195,6 +191,17 @@ static inline int of_node_check_flag(const struct device_node *n, unsigned long
      return test_bit(flag, &n->_flags);
 }
 
+/**
+ * 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)
+{
+     return of_root != NULL && !of_node_check_flag(of_root, OF_EMPTY_ROOT);

Just a side comment, but I think many/all callers of this function could 
just be removed.

I don't love new flags. Another possible way to handle this would be 
checking for "compatible" being present in the root node. I guess this 
is fine as-is for now at least.

Ok. I can add a check for a compatible property. That's probably better
anyway. Should there be a compatible property there to signal that this
DT isn't compatible with anything? I worry about DT overlays injecting a
compatible string into the root node, but maybe that is already
prevented.

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