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@arm.com>
---
 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        | 8 ++++++++
 5 files changed, 15 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..71fc9e00cb 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -400,6 +400,14 @@ 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.
+
 config TRACEBUFFER
 	bool "Enable tracing infrastructure" if EXPERT
 	default y
-- 
2.29.0

On 15.03.2021 07:51, Michal Orzel wrote:
> --- a/xen/common/Kconfig
> +++ b/xen/common/Kconfig
> @@ -400,6 +400,14 @@ 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.

I'm sorry, it should have occurred to me earlier to ask, but: Shouldn't
this text make explicit that this is an optional setting and hence
leaving blank is generally okay? I.e. something along the lines of
what is visible in context above from the prior setting?

Jan