@@ -42,9 +42,14 @@ config OF_FLATTREE
select CRC32
config OF_EARLY_FLATTREE
- bool
+ bool "Functions for accessing Flat Devicetree (FDT) early in boot"
select DMA_DECLARE_COHERENT if HAS_DMA
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
@@ -2,7 +2,7 @@
obj-y = base.o device.o platform.o property.o
obj-$(CONFIG_OF_KOBJ) += kobj.o
obj-$(CONFIG_OF_DYNAMIC) += dynamic.o
-obj-$(CONFIG_OF_FLATTREE) += fdt.o
+obj-$(CONFIG_OF_FLATTREE) += fdt.o empty_root.dtb.o
obj-$(CONFIG_OF_EARLY_FLATTREE) += fdt_address.o
obj-$(CONFIG_OF_PROMTREE) += pdt.o
obj-$(CONFIG_OF_ADDRESS) += address.o
new file mode 100644
@@ -0,0 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/dts-v1/;
+
+/ {
+
+};
@@ -33,6 +33,13 @@
#include "of_private.h"
+/*
+ * __dtb_empty_root_begin[] and __dtb_empty_root_end[] magically created by
+ * cmd_dt_S_dtb in scripts/Makefile.lib
+ */
+extern uint8_t __dtb_empty_root_begin[];
+extern uint8_t __dtb_empty_root_end[];
+
/*
* of_fdt_limit_memory - limit the number of regions in the /memory node
* @limit: maximum entries
@@ -1326,8 +1333,19 @@ bool __init early_init_dt_scan(void *params)
*/
void __init unflatten_device_tree(void)
{
- __unflatten_device_tree(initial_boot_params, NULL, &of_root,
+ if (!initial_boot_params) {
+ initial_boot_params = (void *) __dtb_empty_root_begin;
+ /* fdt_totalsize() will be used for copy size */
+ if (fdt_totalsize(initial_boot_params) >
+ __dtb_empty_root_end - __dtb_empty_root_begin) {
+ pr_err("invalid size in dtb_empty_root\n");
+ return;
+ }
+ unflatten_and_copy_device_tree();
+ } else {
+ __unflatten_device_tree(initial_boot_params, NULL, &of_root,
early_init_dt_alloc_memory_arch, false);
+ }
/* Get pointer to "/chosen" and "/aliases" nodes for use everywhere */
of_alias_scan(early_init_dt_alloc_memory_arch);
@@ -1367,6 +1385,13 @@ void __init unflatten_and_copy_device_tree(void)
unflatten_device_tree();
}
+void __init setup_of(void)
+{
+ /* if architecture did not unflatten devicetree, do it now */
+ if (!of_root)
+ unflatten_device_tree();
+}
+
#ifdef CONFIG_SYSFS
static ssize_t of_fdt_raw_read(struct file *filp, struct kobject *kobj,
struct bin_attribute *bin_attr,
@@ -81,6 +81,7 @@ extern const void *of_flat_dt_match_machine(const void *default_match,
/* Other Prototypes */
extern void unflatten_device_tree(void);
extern void unflatten_and_copy_device_tree(void);
+extern void setup_of(void);
extern void early_init_devtree(void *);
extern void early_get_first_memblock_info(void *, phys_addr_t *);
#else /* CONFIG_OF_EARLY_FLATTREE */
@@ -91,6 +92,7 @@ static inline void early_init_fdt_reserve_self(void) {}
static inline const char *of_flat_dt_get_machine_name(void) { return NULL; }
static inline void unflatten_device_tree(void) {}
static inline void unflatten_and_copy_device_tree(void) {}
+static inline void setup_of(void) {}
#endif /* CONFIG_OF_EARLY_FLATTREE */
#endif /* __ASSEMBLY__ */
@@ -101,6 +101,7 @@
#include <linux/init_syscalls.h>
#include <linux/stackdepot.h>
#include <linux/randomize_kstack.h>
+#include <linux/of_fdt.h>
#include <net/net_namespace.h>
#include <asm/io.h>
@@ -961,6 +962,7 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
pr_notice("%s", linux_banner);
early_security_init();
setup_arch(&command_line);
+ setup_of();
setup_boot_config();
setup_command_line(command_line);
setup_nr_cpu_ids();
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, setup_of() which is called immediately after setup_arch(), and will create the default root node if it does not exist. Signed-off-by: Frank Rowand <frowand.list@gmail.com> --- Please wait for test results from Clement before accepting. Changes since version 2: - change of __dtb_empty_root_* from "void *" to "uint8_t []" Changes since version 1: - refresh for 6.2-rc1 - update Signed-off-by - fix typo in of_fdt.h: s/of_setup/setup_of - unflatten_device_tree(): validate size in header field dtb_empty_root that will be used to copy dtb_empty_root - add Kconfig option to manually select CONFIG_OF_EARLY_FLATTREE drivers/of/Kconfig | 7 ++++++- drivers/of/Makefile | 2 +- drivers/of/empty_root.dts | 6 ++++++ drivers/of/fdt.c | 27 ++++++++++++++++++++++++++- include/linux/of_fdt.h | 2 ++ init/main.c | 2 ++ 6 files changed, 43 insertions(+), 3 deletions(-) create mode 100644 drivers/of/empty_root.dts