[PATCH 0/3] make dtb from 1st stage loader available in barebox

[PATCH 0/3] make dtb from 1st stage loader available in barebox

[Sascha Hauer]

When barebox is chainloaded from another bootloader it usually gets
passed a device tree from the previous bootloader. While this external
device tree is normally not used by barebox, its contents can still be
interesting, so store the device tree at /external-devicetree when
found. This needs board support to pass the external device tree in
handoff data, i.e. a board has to call
handoff_data_add(HANDOFF_DATA_EXTERNAL_DT, dtb, size);
This series adds beagleplay support for this feature as an example.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
Sascha Hauer (3):
      fdt: Add function to check if a pointer contains a fdt
      store external device tree as file
      ARM: beagleplay: put external device tree into handoff data

 arch/arm/boards/beagleplay/lowlevel.c | 14 ++++++++++----
 common/startup.c                      |  8 ++++++++
 include/compressed-dtb.h              | 24 ++++++++++++++++++++++++
 3 files changed, 42 insertions(+), 4 deletions(-)
---
base-commit: 873b572763d38ab4100d218d0a3614f79b596077
change-id: 20241209-ext-dt-handoff-0594e0ae33b2

Best regards,
-- 
Sascha Hauer <s.hauer@pengutronix.de>

[PATCH 1/3] fdt: Add function to check if a pointer contains a fdt

[Sascha Hauer]

When barebox is started 2nd stage from another barebox or U-Boot it
usually gets a device tree passed in a register. We can't rely on this
though, so before assuming a pointer has a device tree we need to
perform some basic checks for being in a certain range, is sufficiently
aligned and actually contains a device tree.
This adds a function performing these checks.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 include/compressed-dtb.h | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/include/compressed-dtb.h b/include/compressed-dtb.h
index 3359d1ee11..cc5fbb2769 100644
--- a/include/compressed-dtb.h
+++ b/include/compressed-dtb.h
@@ -3,6 +3,7 @@
 #define COMPRESSED_DTB_H_
 
 #include <linux/types.h>
+#include <linux/sizes.h>
 #include <asm/unaligned.h>
 
 struct barebox_boarddata_compressed_dtb {
@@ -31,4 +32,27 @@ static inline bool blob_is_fdt(const void *blob)
 	return get_unaligned_be32(blob) == FDT_MAGIC;
 }
 
+static inline bool blob_is_valid_fdt_ptr(const void *blob, unsigned long mem_start,
+					 unsigned long mem_size, unsigned int *fdt_size)
+{
+	unsigned long dtb = (unsigned long)blob;
+	unsigned int size;
+
+	if (!IS_ALIGNED(dtb, 4))
+		return false;
+	if (dtb < mem_start || dtb >= mem_start + mem_size)
+		return false;
+	if (!blob_is_fdt(blob))
+		return false;
+
+	size = be32_to_cpup(blob + 4);
+	if (size > SZ_2M || dtb + size > mem_start + mem_size)
+		return false;
+
+	if (fdt_size)
+		*fdt_size = size;
+
+	return true;
+}
+
 #endif

-- 
2.39.5

[PATCH 2/3] store external device tree as file

[Sascha Hauer]

When barebox is chainloaded from another bootloader it usually gets
passed a device tree from the previous bootloader. While this external
device tree is normally not used by barebox, its contents can still be
interesting, so store the device tree at /external-devicetree when
found. This needs board support to pass the external device tree in
handoff data, i.e. a board has to call
handoff_data_add(HANDOFF_DATA_EXTERNAL_DT, dtb, size);

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 common/startup.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/common/startup.c b/common/startup.c
index b311b77418..abdc0c2db0 100644
--- a/common/startup.c
+++ b/common/startup.c
@@ -40,6 +40,8 @@
 #include <net.h>
 #include <efi/efi-mode.h>
 #include <bselftest.h>
+#include <pbl/handoff-data.h>
+#include <libfile.h>
 
 extern initcall_t __barebox_initcalls_start[], __barebox_early_initcalls_end[],
 		  __barebox_initcalls_end[];
@@ -246,6 +248,8 @@ static int run_init(void)
 	struct stat s;
 	glob_t g;
 	int i, ret;
+	size_t size;
+	void *ext_dtb;
 
 	setenv("PATH", "/env/bin");
 	export("PATH");
@@ -289,6 +293,10 @@ static int run_init(void)
 		globfree(&g);
 	}
 
+	ext_dtb = handoff_data_get_entry(HANDOFF_DATA_EXTERNAL_DT, &size);
+	if (ext_dtb)
+		write_file("/external-devicetree", ext_dtb, size);
+
 	/* source matching script in /env/bmode/ */
 	bmode = reboot_mode_get();
 	if (bmode) {

-- 
2.39.5

[PATCH 3/3] ARM: beagleplay: put external device tree into handoff data

[Sascha Hauer]

Pass the dtb from 1st stage loader to barebox using handoff data.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 arch/arm/boards/beagleplay/lowlevel.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/arch/arm/boards/beagleplay/lowlevel.c b/arch/arm/boards/beagleplay/lowlevel.c
index 9d76dbd0a2..228484bf4e 100644
--- a/arch/arm/boards/beagleplay/lowlevel.c
+++ b/arch/arm/boards/beagleplay/lowlevel.c
@@ -5,21 +5,27 @@
 #include <asm/barebox-arm.h>
 #include <debug_ll.h>
 #include <pbl.h>
+#include <pbl/handoff-data.h>
+#include <compressed-dtb.h>
 
 /* Called from assembly */
-void beagleplay(void);
+void beagleplay(void *dtb);
 
-static noinline void beagleplay_continue(void)
+static noinline void beagleplay_continue(void *dtb)
 {
 	unsigned long membase, memsize;
 	extern char __dtb_k3_am625_beagleplay_start[];
+	unsigned int size;
 
 	fdt_find_mem(__dtb_k3_am625_beagleplay_start, &membase, &memsize);
 
+	if (blob_is_valid_fdt_ptr(dtb, membase, memsize, &size))
+		handoff_data_add(HANDOFF_DATA_EXTERNAL_DT, dtb, size);
+
 	barebox_arm_entry(membase, memsize, __dtb_k3_am625_beagleplay_start);
 }
 
-void beagleplay(void)
+void beagleplay(void *dtb)
 {
 	putc_ll('>');
 
@@ -29,5 +35,5 @@ void beagleplay(void)
 
 	setup_c();
 
-	beagleplay_continue();
+	beagleplay_continue(dtb);
 }

-- 
2.39.5

Re: [PATCH 0/3] make dtb from 1st stage loader available in barebox

[Sascha Hauer]

On Mon, 09 Dec 2024 15:28:10 +0100, Sascha Hauer wrote:
> When barebox is chainloaded from another bootloader it usually gets
> passed a device tree from the previous bootloader. While this external
> device tree is normally not used by barebox, its contents can still be
> interesting, so store the device tree at /external-devicetree when
> found. This needs board support to pass the external device tree in
> handoff data, i.e. a board has to call
> handoff_data_add(HANDOFF_DATA_EXTERNAL_DT, dtb, size);
> This series adds beagleplay support for this feature as an example.
> 
> [...]

Applied, thanks!

[1/3] fdt: Add function to check if a pointer contains a fdt
      https://git.pengutronix.de/cgit/barebox/commit/?id=abcd32a3e85f (link may not be stable)
[2/3] store external device tree as file
      https://git.pengutronix.de/cgit/barebox/commit/?id=78c3e4145aa6 (link may not be stable)
[3/3] ARM: beagleplay: put external device tree into handoff data
      https://git.pengutronix.de/cgit/barebox/commit/?id=0e62b0b1ecb2 (link may not be stable)

Best regards,
-- 
Sascha Hauer <s.hauer@pengutronix.de>