linux-kernel - Re: [PATCH V2 XRT Alveo Infrastructure 4/9] of: create empty of root

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Date:   Mon, 29 Nov 2021 19:59:46 -0600
From:   Rob Herring <robh@...nel.org>
To:     Lizhi Hou <lizhi.hou@...inx.com>
Cc:     linux-kernel@...r.kernel.org, linux-fpga@...r.kernel.org,
        maxz@...inx.com, sonal.santan@...inx.com, yliu@...inx.com,
        michal.simek@...inx.com, stefanos@...inx.com,
        devicetree@...r.kernel.org, trix@...hat.com, mdf@...nel.org,
        dwmw2@...radead.org, Max Zhen <max.zhen@...inx.com>
Subject: Re: [PATCH V2 XRT Alveo Infrastructure 4/9] of: create empty of root

On Fri, Nov 19, 2021 at 02:24:07PM -0800, Lizhi Hou wrote:
> When OF_FLATTREE is selected and there is not a device tree, create an
> empty device tree root node. of/unittest.c code is referenced.

What does the last sentence mean? You copied the code? If so, that's a 
sign you should refactor the unittest code to use this.

> 
> Signed-off-by: Sonal Santan <sonal.santan@...inx.com>
> Signed-off-by: Max Zhen <max.zhen@...inx.com>
> Signed-off-by: Lizhi Hou <lizhi.hou@...inx.com>
> ---
>  drivers/of/Makefile        |  2 +-
>  drivers/of/fdt.c           | 20 ++++++++++++++++++++
>  drivers/of/fdt_default.dts |  5 +++++
>  drivers/of/of_private.h    |  5 +++++
>  4 files changed, 31 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/of/fdt_default.dts
> 
> diff --git a/drivers/of/Makefile b/drivers/of/Makefile
> index c13b982084a3..815f5220465b 100644
> --- a/drivers/of/Makefile
> +++ b/drivers/of/Makefile
> @@ -2,7 +2,7 @@
>  obj-y = base.o device.o platform.o property.o
>  obj-$(CONFIG_OF_KOBJ) += kobj.o
>  obj-$(CONFIG_OF_DYNAMIC) += dynamic.o
> -obj-$(CONFIG_OF_FLATTREE) += fdt.o
> +obj-$(CONFIG_OF_FLATTREE) += fdt.o fdt_default.dtb.o
>  obj-$(CONFIG_OF_EARLY_FLATTREE) += fdt_address.o
>  obj-$(CONFIG_OF_PROMTREE) += pdt.o
>  obj-$(CONFIG_OF_ADDRESS)  += address.o
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index d64445e43ceb..3d6e4543419e 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -481,6 +481,26 @@ void *of_fdt_unflatten_tree(const unsigned long *blob,
>  }
>  EXPORT_SYMBOL_GPL(of_fdt_unflatten_tree);
>  
> +static int __init of_fdt_root_init(void)
> +{
> +	struct device_node *np;
> +
> +	if (of_root)
> +		return 0;
> +
> +	if (!of_fdt_unflatten_tree((const unsigned long *)__dtb_fdt_default_begin,
> +				   NULL, &of_root)) {
> +		pr_warn("%s: unflatten default tree failed\n", __func__);
> +		return -ENODATA;
> +	}
> +
> +	for_each_of_allnodes(np)
> +		__of_attach_node_sysfs(np);
> +
> +	return 0;
> +}
> +late_initcall(of_fdt_root_init);
> +
>  /* Everything below here references initial_boot_params directly. */
>  int __initdata dt_root_addr_cells;
>  int __initdata dt_root_size_cells;
> diff --git a/drivers/of/fdt_default.dts b/drivers/of/fdt_default.dts
> new file mode 100644
> index 000000000000..d1f12a76dfc6
> --- /dev/null
> +++ b/drivers/of/fdt_default.dts
> @@ -0,0 +1,5 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/dts-v1/;
> +
> +/ {
> +};
> diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
> index 631489f7f8c0..47c6bb47ef25 100644
> --- a/drivers/of/of_private.h
> +++ b/drivers/of/of_private.h
> @@ -41,6 +41,11 @@ extern struct mutex of_mutex;
>  extern struct list_head aliases_lookup;
>  extern struct kset *of_kset;
>  
> +#if defined(CONFIG_OF_FLATTREE)
> +extern u8 __dtb_fdt_default_begin[];
> +extern u8 __dtb_fdt_default_end[];
> +#endif
> +
>  #if defined(CONFIG_OF_DYNAMIC)
>  extern int of_property_notify(int action, struct device_node *np,
>  			      struct property *prop, struct property *old_prop);
> -- 
> 2.27.0
> 
>