[U-Boot] [PATCH 06/17] dm: Add callback to modify the device tree

[Mario Six]

Certain boards come in different variations by way of utilizing daughter
boards, for example. These boards might contain additional chips, which
are added to the main board's busses, e.g. I2C.

The device tree support for such boards would either, quite naturally,
employ the overlay mechanism to add such chips to the tree, or would use
one large default device tree, and delete the devices that are actually
not present.

Regardless of approach, even on the U-Boot level, a modification of the
device tree is a prerequisite to have such modular families of boards
supported properly.

Therefore, we add an option to make the U-Boot device tree (the actual
copy later used by the driver model) writeable, and add a callback
method that allows boards to modify the device tree at an early stage,
at which, hopefully, also the application of device tree overlays will
be possible.

Signed-off-by: Mario Six <mario.six at gdsys.cc>
---
 common/board_f.c                  |  3 +++
 dts/Kconfig                       | 10 ++++++++++
 include/asm-generic/global_data.h |  4 ++++
 include/common.h                  |  1 +
 4 files changed, 18 insertions(+)

diff --git a/common/board_f.c b/common/board_f.c
index 4b74835..cda5aae 100644
--- a/common/board_f.c
+++ b/common/board_f.c
@@ -1034,6 +1034,9 @@ static init_fnc_t init_sequence_f[] = {
 #ifdef CONFIG_SYS_EXTBDINFO
 	setup_board_extra,
 #endif
+#ifdef CONFIG_OF_BOARD_FIXUP
+	board_fix_fdt,
+#endif
 	INIT_FUNC_WATCHDOG_RESET
 	reloc_fdt,
 	setup_reloc,
diff --git a/dts/Kconfig b/dts/Kconfig
index 4b7d8b1..3f64eda 100644
--- a/dts/Kconfig
+++ b/dts/Kconfig
@@ -14,6 +14,16 @@ config OF_CONTROL
 	  This feature provides for run-time configuration of U-Boot
 	  via a flattened device tree.
 
+config OF_BOARD_FIXUP
+	bool "Board-specific manipulation of Device Tree"
+	help
+	  In certain circumstances it is necessary to be able to modify
+	  U-Boot's device tree (e.g. to delete device from it). This option
+	  make the Device Tree writeable and provides a board-specific
+	  "board_fix_fdt" callback (called during pre-relocation time), which
+	  enables the board initialization to modifiy the Device Tree. The
+	  modified copy is subsequently used by U-Boot after relocation.
+
 config SPL_OF_CONTROL
 	bool "Enable run-time configuration via Device Tree in SPL"
 	depends on SPL && OF_CONTROL
diff --git a/include/asm-generic/global_data.h b/include/asm-generic/global_data.h
index e02863d..f566186 100644
--- a/include/asm-generic/global_data.h
+++ b/include/asm-generic/global_data.h
@@ -69,7 +69,11 @@ typedef struct global_data {
 	struct udevice	*timer;		/* Timer instance for Driver Model */
 #endif
 
+#ifdef CONFIG_OF_BOARD_FIXUP
+	void *fdt_blob;			/* Our device tree, NULL if none */
+#else
 	const void *fdt_blob;		/* Our device tree, NULL if none */
+#endif
 	void *new_fdt;			/* Relocated FDT */
 	unsigned long fdt_size;		/* Space reserved for relocated FDT */
 	struct jt_funcs *jt;		/* jump table */
diff --git a/include/common.h b/include/common.h
index a8d833b..293ce23 100644
--- a/include/common.h
+++ b/include/common.h
@@ -502,6 +502,7 @@ extern ssize_t spi_write (uchar *, int, uchar *, int);
 
 /* $(BOARD)/$(BOARD).c */
 int board_early_init_f (void);
+int board_fix_fdt (void);
 int board_late_init (void);
 int board_postclk_init (void); /* after clocks/timebase, before env/serial */
 int board_early_init_r (void);
-- 
2.9.0