Re: [PATCH V1 Create empty OF root 1/1] of: create empty of root

[Xu Yilun]

On Tue, Jan 25, 2022 at 09:48:07PM -0800, Lizhi Hou wrote:
> Add OF_EMPTY_ROOT config. When it is selected and there is not a device
> tree, create an empty device tree root node.

Maybe add some description about why a empty device tree root node is
needed. Note that the Patch #0 will not be present in the repo when the
series will be merged, so add your description here please.

> 
> Signed-off-by: Sonal Santan <sonal.santan@xxxxxxxxxx>
> Signed-off-by: Max Zhen <max.zhen@xxxxxxxxxx>
> Signed-off-by: Lizhi Hou <lizhi.hou@xxxxxxxxxx>
> ---
>  drivers/of/Kconfig         |  3 +++
>  drivers/of/Makefile        |  1 +
>  drivers/of/of_empty_root.c | 51 ++++++++++++++++++++++++++++++++++++++
>  3 files changed, 55 insertions(+)
>  create mode 100644 drivers/of/of_empty_root.c
> 
> diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
> index 80b5fd44ab1c..42afb126f91a 100644
> --- a/drivers/of/Kconfig
> +++ b/drivers/of/Kconfig
> @@ -94,4 +94,7 @@ config OF_DMA_DEFAULT_COHERENT
>  	# arches should select this if DMA is coherent by default for OF devices
>  	bool
>  
> +config OF_EMPTY_ROOT
> +	bool

Also some descriptions for better understanding?

Thanks,
Yilun

> +
>  endif # OF
> diff --git a/drivers/of/Makefile b/drivers/of/Makefile
> index e0360a44306e..c65364f32935 100644
> --- a/drivers/of/Makefile
> +++ b/drivers/of/Makefile
> @@ -12,6 +12,7 @@ obj-$(CONFIG_OF_RESERVED_MEM) += of_reserved_mem.o
>  obj-$(CONFIG_OF_RESOLVE)  += resolver.o
>  obj-$(CONFIG_OF_OVERLAY) += overlay.o
>  obj-$(CONFIG_OF_NUMA) += of_numa.o
> +obj-$(CONFIG_OF_EMPTY_ROOT) += of_empty_root.o
>  
>  ifdef CONFIG_KEXEC_FILE
>  ifdef CONFIG_OF_FLATTREE
> diff --git a/drivers/of/of_empty_root.c b/drivers/of/of_empty_root.c
> new file mode 100644
> index 000000000000..5c429c7a27bd
> --- /dev/null
> +++ b/drivers/of/of_empty_root.c
> @@ -0,0 +1,51 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2022 Xilinx, Inc.
> + */
> +
> +#include <linux/of.h>
> +#include <linux/slab.h>
> +
> +#include "of_private.h"
> +
> +static int __init of_root_init(void)
> +{
> +	struct property *prop = NULL;
> +	struct device_node *node;
> +	__be32 *val = NULL;
> +
> +	if (of_root)
> +		return 0;
> +
> +	pr_info("Create empty OF root node\n");
> +	node = kzalloc(sizeof(*node), GFP_KERNEL);
> +	if (!node)
> +		return -ENOMEM;
> +	of_node_init(node);
> +	node->full_name = "/";
> +
> +	prop = kcalloc(2, sizeof(*prop), GFP_KERNEL);
> +	if (!prop)
> +		return -ENOMEM;
> +
> +	val = kzalloc(sizeof(*val), GFP_KERNEL);
> +	if (!val)
> +		return -ENOMEM;
> +	*val = cpu_to_be32(sizeof(void *) / sizeof(u32));
> +
> +	prop->name = "#address-cells";
> +	prop->value = val;
> +	prop->length = sizeof(u32);
> +	of_add_property(node, prop);
> +	prop++;
> +	prop->name = "#size-cells";
> +	prop->value = val;
> +	prop->length = sizeof(u32);
> +	of_add_property(node, prop);
> +	of_root = node;
> +	for_each_of_allnodes(node)
> +		__of_attach_node_sysfs(node);
> +
> +	return 0;
> +}
> +pure_initcall(of_root_init);
> -- 
> 2.27.0