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

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Michal,

> On 15 Mar 2021, at 09:23, Michal Orzel <Michal.Orzel@xxxxxxx> wrote:
> 
> 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>
Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>

The use of ifnes and PROVIDE is very clever :-)

Cheers
Bertrand


> ---
> 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
>