[PATCH] common: Add Kconfig option for FDT mem alignment

[Heinrich Schuchardt]

On 4/13/20 10:03 AM, Michal Simek wrote:
> From: Ashok Reddy Soma <ashok.reddy.soma at xilinx.com>
>
> FDT memory is aligned by 4KB. This is hardcoded in common/board_f.c.
> Add Kconfig option, assign default value of 0x1000 and enable option to
> change this value.

Please, describe why this patch is needed.

>
> Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma at xilinx.com>
> Signed-off-by: Michal Simek <michal.simek at xilinx.com>
> ---
>
>  common/board_f.c | 3 ++-
>  dts/Kconfig      | 7 +++++++
>  2 files changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/common/board_f.c b/common/board_f.c
> index 82a164752aa3..928874e03555 100644
> --- a/common/board_f.c
> +++ b/common/board_f.c
> @@ -546,7 +546,8 @@ static int reserve_fdt(void)
>  	 * will be relocated with other data.
>  	 */
>  	if (gd->fdt_blob) {
> -		gd->fdt_size = ALIGN(fdt_totalsize(gd->fdt_blob) + 0x1000, 32);
> +		gd->fdt_size = ALIGN(fdt_totalsize(gd->fdt_blob) +
> +				     CONFIG_FDT_MEM_ALIGN_SIZE, 32);
>
>  		gd->start_addr_sp -= gd->fdt_size;
>  		gd->new_fdt = map_sysmem(gd->start_addr_sp, gd->fdt_size);

This change does not relate to the commit message. You are not adjusting
the alignment of the device tree location. You are adjusting the size of
the memory available for the device tree.

reserve_fdt() is called after reserve_global_data() where we have:
gd->start_addr_sp -= sizeof(gd_t).

A typical debug output from reserve_global_data() is:
Reserving 544 Bytes for Global Data at: bf740d98

So in this case the device tree will have an alignment of 8 no matter
what power of 2 (>= 8) you choose for CONFIG_FDT_MEM_ALIGN_SIZE.

What about other places where we allocate memory for device trees like
copy_fdt() in cmd/bootefi.?

> diff --git a/dts/Kconfig b/dts/Kconfig
> index 046a54a17366..696c0b71afaf 100644
> --- a/dts/Kconfig
> +++ b/dts/Kconfig
> @@ -121,6 +121,13 @@ config DEFAULT_DEVICE_TREE
>  	  It can be overridden from the command line:
>  	  $ make DEVICE_TREE=<device-tree-name>
>
> +config FDT_MEM_ALIGN_SIZE
> +	hex "FDT memory alignment size"
> +	default 0x1000
> +	help
> +	  This option is used to set the default alignment when reserving memory

%s/is used to set the default alignment/sets the alignment/

Please, mention if this value should be a power of 2.

Best regards

Heinrich

> +	  for fdt.
> +
>  config OF_LIST
>  	string "List of device tree files to include for DT control"
>  	depends on SPL_LOAD_FIT || MULTI_DTB_FIT
>