This series is a different implementation to achieve the goals of
https://lore.kernel.org/r/[email protected]
In order to apply overlays or create new nodes under the root node, the
kernel expects of_root to be set. On some system where a device-tree was
not provided by firmware (x86 for instance) if CONFIG_OF is enabled,
then we will end up with a null of_root. This series adds support to
create this root node using a builtin dtb and removes the manual
creation of the root node done in unittests.c.
Changes since version 1: (patch 1/2)
- 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
Changes since version 1: (patch 2/2)
- refresh for 6.2-rc1
- update Signed-off-by
- fix formatting error (leading space) in patch comment
Frank Rowand (2):
of: create of_root if no dtb provided
of: unittest: treat missing of_root as error instead of fixing up
drivers/of/Kconfig | 7 ++++++-
drivers/of/Makefile | 2 +-
drivers/of/empty_root.dts | 6 ++++++
drivers/of/fdt.c | 27 ++++++++++++++++++++++++++-
drivers/of/unittest.c | 16 ++++++----------
include/linux/of_fdt.h | 2 ++
init/main.c | 2 ++
7 files changed, 49 insertions(+), 13 deletions(-)
create mode 100644 drivers/of/empty_root.dts
--
Frank Rowand <[email protected]>
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 <[email protected]>
---
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 <[email protected]>
setup_of() now ensures that of_root node is populated with the
root of a default devicetree. Remove the unittest code that
created of_root if it was missing. Verify that of_root is
valid before attempting to attach the testcase-data subtree.
Signed-off-by: Frank Rowand <[email protected]>
---
Changes since version 1:
- refresh for 6.2-rc1
- update Signed-off-by
- fix formatting error (leading space) in patch comment
drivers/of/unittest.c | 16 ++++++----------
1 file changed, 6 insertions(+), 10 deletions(-)
diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index bc0f1e50a4be..006713511c53 100644
--- a/drivers/of/unittest.c
+++ b/drivers/of/unittest.c
@@ -1469,20 +1469,16 @@ static int __init unittest_data_add(void)
return -EINVAL;
}
- if (!of_root) {
- of_root = unittest_data_node;
- for_each_of_allnodes(np)
- __of_attach_node_sysfs(np);
- of_aliases = of_find_node_by_path("/aliases");
- of_chosen = of_find_node_by_path("/chosen");
- of_overlay_mutex_unlock();
- return 0;
- }
-
EXPECT_BEGIN(KERN_INFO,
"Duplicate name in testcase-data, renamed to \"duplicate-name#1\"");
/* attach the sub-tree to live tree */
+ if (!of_root) {
+ pr_warn("%s: no live tree to attach sub-tree\n", __func__);
+ kfree(unittest_data);
+ return -ENODEV;
+ }
+
np = unittest_data_node->child;
while (np) {
struct device_node *next = np->sibling;
--
Frank Rowand <[email protected]>
Le Wed, 22 Feb 2023 16:10:49 -0600,
Frank Rowand <[email protected]> a écrit :
> This series is a different implementation to achieve the goals of
> https://lore.kernel.org/r/[email protected]
>
> In order to apply overlays or create new nodes under the root node, the
> kernel expects of_root to be set. On some system where a device-tree was
> not provided by firmware (x86 for instance) if CONFIG_OF is enabled,
> then we will end up with a null of_root. This series adds support to
> create this root node using a builtin dtb and removes the manual
> creation of the root node done in unittests.c.
Hi Frank, I'm currently testing your series and I encountered some
crashes at boot. Looks like it comes from the
early_init_dt_alloc_memory_arch() that calls panic. Maybe the memblock
allocator is not ready yet. Please note that I'm testing it on a x86
kernel. I'll investigate that.
Regarding the series itself it seems ok to me.
Thanks,
Clément
>
> Changes since version 1: (patch 1/2)
> - 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
>
> Changes since version 1: (patch 2/2)
> - refresh for 6.2-rc1
> - update Signed-off-by
> - fix formatting error (leading space) in patch comment
>
> Frank Rowand (2):
> of: create of_root if no dtb provided
> of: unittest: treat missing of_root as error instead of fixing up
>
> drivers/of/Kconfig | 7 ++++++-
> drivers/of/Makefile | 2 +-
> drivers/of/empty_root.dts | 6 ++++++
> drivers/of/fdt.c | 27 ++++++++++++++++++++++++++-
> drivers/of/unittest.c | 16 ++++++----------
> include/linux/of_fdt.h | 2 ++
> init/main.c | 2 ++
> 7 files changed, 49 insertions(+), 13 deletions(-)
> create mode 100644 drivers/of/empty_root.dts
>
--
Clément Léger,
Embedded Linux and Kernel engineer at Bootlin
https://bootlin.com
Le Wed, 22 Feb 2023 16:10:50 -0600,
Frank Rowand <[email protected]> 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 <[email protected]>
> ---
>
> 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 <[email protected]> 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 <[email protected]>
>> ---
>>
>> 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();
>
>
>