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>
---
There are checkpatch warnings. I have reviewed them and feel
they can be ignored.
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
diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
index 80b5fd44ab1c..591cfe386727 100644
--- a/drivers/of/Kconfig
+++ b/drivers/of/Kconfig
@@ -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
diff --git a/drivers/of/Makefile b/drivers/of/Makefile
index e0360a44306e..cbae92c5ed02 100644
--- a/drivers/of/Makefile
+++ b/drivers/of/Makefile
@@ -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
diff --git a/drivers/of/empty_root.dts b/drivers/of/empty_root.dts
new file mode 100644
index 000000000000..cf9e97a60f48
--- /dev/null
+++ b/drivers/of/empty_root.dts
@@ -0,0 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/dts-v1/;
+
+/ {
+
+};
diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index b2272bccf85c..0d2f6d016b7e 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -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 void *__dtb_empty_root_begin;
+extern void *__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,
diff --git a/include/linux/of_fdt.h b/include/linux/of_fdt.h
index d69ad5bb1eb1..f0dc46d576da 100644
--- a/include/linux/of_fdt.h
+++ b/include/linux/of_fdt.h
@@ -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__ */
diff --git a/init/main.c b/init/main.c
index e1c3911d7c70..31e0931b5134 100644
--- a/init/main.c
+++ b/init/main.c
@@ -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();
--
Frank Rowand <frowand.list@gmail.com>
Le Wed, 22 Feb 2023 16:10:50 -0600, Frank Rowand <frowand.list@gmail.com> a écrit : > 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> > --- > > There are checkpatch warnings. I have reviewed them and feel > they can be ignored. > > 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 > > diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig > index 80b5fd44ab1c..591cfe386727 100644 > --- a/drivers/of/Kconfig > +++ b/drivers/of/Kconfig > @@ -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 > diff --git a/drivers/of/Makefile b/drivers/of/Makefile > index e0360a44306e..cbae92c5ed02 100644 > --- a/drivers/of/Makefile > +++ b/drivers/of/Makefile > @@ -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 > diff --git a/drivers/of/empty_root.dts b/drivers/of/empty_root.dts > new file mode 100644 > index 000000000000..cf9e97a60f48 > --- /dev/null > +++ b/drivers/of/empty_root.dts > @@ -0,0 +1,6 @@ > +// SPDX-License-Identifier: GPL-2.0-only > +/dts-v1/; > + > +/ { > + > +}; > diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c > index b2272bccf85c..0d2f6d016b7e 100644 > --- a/drivers/of/fdt.c > +++ b/drivers/of/fdt.c > @@ -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 void *__dtb_empty_root_begin; > +extern void *__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; The crash I encountered was actually not due to memblock alloc but to this usage/declaration of the embedded dtb pointers which is wrong. Either declare it as: extern char __dtb_empty_root_begin[]; extern char __dtb_empty_root_end[]; and keep the existing usage in this function or keep the existing declaration but modify this function to use &__dtb_empty_root_begin With this modification, I finally have an empty device-tree present on my system: $ dtc -I fs -O dts /sys/firmware/devicetree/ /dts-v1/; / { }; Thanks, Clément > + /* 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, > diff --git a/include/linux/of_fdt.h b/include/linux/of_fdt.h > index d69ad5bb1eb1..f0dc46d576da 100644 > --- a/include/linux/of_fdt.h > +++ b/include/linux/of_fdt.h > @@ -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__ */ > diff --git a/init/main.c b/init/main.c > index e1c3911d7c70..31e0931b5134 100644 > --- a/init/main.c > +++ b/init/main.c > @@ -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(); -- Clément Léger, Embedded Linux and Kernel engineer at Bootlin https://bootlin.com
On 2/23/23 05:34, Clément Léger wrote: > Le Wed, 22 Feb 2023 16:10:50 -0600, > Frank Rowand <frowand.list@gmail.com> a écrit : > >> 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> >> --- >> >> There are checkpatch warnings. I have reviewed them and feel >> they can be ignored. >> >> 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 >> >> diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig >> index 80b5fd44ab1c..591cfe386727 100644 >> --- a/drivers/of/Kconfig >> +++ b/drivers/of/Kconfig >> @@ -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 >> diff --git a/drivers/of/Makefile b/drivers/of/Makefile >> index e0360a44306e..cbae92c5ed02 100644 >> --- a/drivers/of/Makefile >> +++ b/drivers/of/Makefile >> @@ -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 >> diff --git a/drivers/of/empty_root.dts b/drivers/of/empty_root.dts >> new file mode 100644 >> index 000000000000..cf9e97a60f48 >> --- /dev/null >> +++ b/drivers/of/empty_root.dts >> @@ -0,0 +1,6 @@ >> +// SPDX-License-Identifier: GPL-2.0-only >> +/dts-v1/; >> + >> +/ { >> + >> +}; >> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c >> index b2272bccf85c..0d2f6d016b7e 100644 >> --- a/drivers/of/fdt.c >> +++ b/drivers/of/fdt.c >> @@ -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 void *__dtb_empty_root_begin; >> +extern void *__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; > > The crash I encountered was actually not due to memblock alloc but to > this usage/declaration of the embedded dtb pointers which is wrong. > > Either declare it as: > > extern char __dtb_empty_root_begin[]; > extern char __dtb_empty_root_end[]; Thanks for catching this, and the fix. I will change to uint8_t instead of char, consistent with the use in drivers/of/unittest.c -Frank > > and keep the existing usage in this function or keep the existing > declaration but modify this function to use &__dtb_empty_root_begin > > With this modification, I finally have an empty device-tree present on > my system: > > $ dtc -I fs -O dts /sys/firmware/devicetree/ > /dts-v1/; > > / { > }; > > Thanks, > > Clément > >> + /* 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, >> diff --git a/include/linux/of_fdt.h b/include/linux/of_fdt.h >> index d69ad5bb1eb1..f0dc46d576da 100644 >> --- a/include/linux/of_fdt.h >> +++ b/include/linux/of_fdt.h >> @@ -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__ */ >> diff --git a/init/main.c b/init/main.c >> index e1c3911d7c70..31e0931b5134 100644 >> --- a/init/main.c >> +++ b/init/main.c >> @@ -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(); > > >
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