[PATCH v7] arm: Add Kconfig entry to select CONFIG_DTB_FILE

[Michal Orzel <michal.orzel@xxxxxxx>]

Currently in order to link existing DTB into Xen image
we need to either specify option CONFIG_DTB_FILE on the
command line or manually add it into .config.
Add Kconfig entry: CONFIG_DTB_FILE
to be able to provide the path to DTB we want to embed
into Xen image. If no path provided - the dtb will not
be embedded.

Remove the line: AFLAGS-y += -DCONFIG_DTB_FILE=\"$(CONFIG_DTB_FILE)\"
as it is not needed since Kconfig will define it in a header
with all the other config options.

Make a change in the linker script from:
_sdtb = .;
to:
PROVIDE(_sdtb = .);
to avoid creation of _sdtb if there is no reference to it.

Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
---
 xen/arch/arm/Makefile     |  5 ++---
 xen/arch/arm/arm32/head.S |  4 ++--
 xen/arch/arm/arm64/head.S |  4 ++--
 xen/arch/arm/xen.lds.S    |  4 +---
 xen/common/Kconfig        | 10 ++++++++++
 5 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/xen/arch/arm/Makefile b/xen/arch/arm/Makefile
index 16e6523e2c..46e6a95fec 100644
--- a/xen/arch/arm/Makefile
+++ b/xen/arch/arm/Makefile
@@ -68,9 +68,8 @@ extra-y += $(TARGET_SUBARCH)/head.o
 
 #obj-bin-y += ....o
 
-ifdef CONFIG_DTB_FILE
+ifneq ($(CONFIG_DTB_FILE),"")
 obj-y += dtb.o
-AFLAGS-y += -DCONFIG_DTB_FILE=\"$(CONFIG_DTB_FILE)\"
 endif
 
 ALL_OBJS := $(TARGET_SUBARCH)/head.o $(ALL_OBJS)
@@ -137,7 +136,7 @@ asm-offsets.s: $(TARGET_SUBARCH)/asm-offsets.c
 xen.lds: xen.lds.S
        $(CPP) -P $(a_flags) -MQ $@ -o $@ $<
 
-dtb.o: $(CONFIG_DTB_FILE)
+dtb.o: $(patsubst "%",%,$(CONFIG_DTB_FILE))
 
 .PHONY: clean
 clean::
diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
index c404fa973e..50f019ed98 100644
--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -156,10 +156,10 @@ past_zImage:
         sub   r10, r9, r0            /* r10 := phys-offset */
 
         /* Using the DTB in the .dtb section? */
-#ifdef CONFIG_DTB_FILE
+.ifnes CONFIG_DTB_FILE,""
         ldr   r8, =_sdtb
         add   r8, r10                /* r8 := paddr(DTB) */
-#endif
+.endif
 
         /* Initialize the UART if earlyprintk has been enabled. */
 #ifdef CONFIG_EARLY_PRINTK
diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index 5d44667bd8..f38a8dfca7 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -296,9 +296,9 @@ real_start_efi:
         sub   x20, x19, x0           /* x20 := phys-offset */
 
         /* Using the DTB in the .dtb section? */
-#ifdef CONFIG_DTB_FILE
+.ifnes CONFIG_DTB_FILE,""
         load_paddr x21, _sdtb
-#endif
+.endif
 
         /* Initialize the UART if earlyprintk has been enabled. */
 #ifdef CONFIG_EARLY_PRINTK
diff --git a/xen/arch/arm/xen.lds.S b/xen/arch/arm/xen.lds.S
index 004b182acb..540a7ccc9d 100644
--- a/xen/arch/arm/xen.lds.S
+++ b/xen/arch/arm/xen.lds.S
@@ -220,11 +220,9 @@ SECTIONS
   } :text
   _end = . ;
 
-#ifdef CONFIG_DTB_FILE
   /* Section for the device tree blob (if any). */
-  _sdtb = .;
+  PROVIDE(_sdtb = .);
   .dtb : { *(.dtb) } :text
-#endif
 
   /* Sections to be discarded */
   /DISCARD/ : {
diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index eb953d171e..a1755cd380 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -400,6 +400,16 @@ config DOM0_MEM
 
          Leave empty if you are not sure what to specify.
 
+config DTB_FILE
+       string "Absolute path to device tree blob"
+       depends on HAS_DEVICE_TREE
+       help
+         When using a bootloader that has no device tree support or when there
+         is no bootloader at all, use this option to specify the absolute path
+         to a device tree that will be linked directly inside Xen binary.
+
+         This is an optional config. Leave empty if not needed.
+
 config TRACEBUFFER
        bool "Enable tracing infrastructure" if EXPERT
        default y
-- 
2.29.0