linux-kernel - Re: [PATCH 1/2] of: create of

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Date:   Fri, 24 Jun 2022 14:13:20 +0200
From:   Clément Léger <clement.leger@...tlin.com>
To:     frowand.list@...il.com
Cc:     Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Lizhi Hou <lizhi.hou@...inx.com>,
        Allan Nielsen <allan.nielsen@...rochip.com>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Steen Hegelund <steen.hegelund@...rochip.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 1/2]  of: create of_root if no dtb provided

Le Thu, 23 Jun 2022 22:43:26 -0500,
frowand.list@...il.com a écrit :

>  
> +/*
> + * __dtb_empty_root_begin[] magically created by cmd_dt_S_dtb in
> + * scripts/Makefile.lib
> + */
> +extern void *__dtb_empty_root_begin;
> +
>  /*
>   * of_fdt_limit_memory - limit the number of regions in the /memory node
>   * @limit: maximum entries
> @@ -1332,8 +1338,13 @@ bool __init early_init_dt_scan(void *params)
>   */
>  void __init unflatten_device_tree(void)
>  {

Hi Frank,

This function is only defined when CONFIG_OF_EARLY_FLATTREE is enabled.
Which means that on platforms that do not select this, the default
empty device-tree creation will not be done.

This configuration option is selected by the platform and not by the
user. On x86, only one config enables this (X86_INTEL_CE) which means
this won't work on all the other platforms even if CONFIG_OF is
selected. I would need this to work by only selected CONFIG_OF.
That's why I decided to add the of_root creation in of_core_init()
using a function (of_fdt_unflatten()) that is provided if CONFIG_OF is
defined.

> -	__unflatten_device_tree(initial_boot_params, NULL, &of_root,
> +	if (!initial_boot_params) {
> +		initial_boot_params = (void *) __dtb_empty_root_begin;
> +		unflatten_and_copy_device_tree();
> +	} else {
> +		__unflatten_device_tree(initial_boot_params, NULL, &of_root,
>  				early_init_dt_alloc_memory_arch, false);
> +	}
>  
>  	/* Get pointer to "/chosen" and "/aliases" nodes for use everywhere */
>  	of_alias_scan(early_init_dt_alloc_memory_arch);
> @@ -1373,6 +1384,12 @@ void __init unflatten_and_copy_device_tree(void)
>  	unflatten_device_tree();
>  }
>  
> +void __init setup_of(void)
> +{
> +	if (!of_root)
> +		unflatten_device_tree();
> +}
> +
>  #ifdef CONFIG_SYSFS
>  static ssize_t of_fdt_raw_read(struct file *filp, struct kobject *kobj,
>  			       struct bin_attribute *bin_attr,
> diff --git a/include/linux/of_fdt.h b/include/linux/of_fdt.h
> index d69ad5bb1eb1..4566876db351 100644
> --- a/include/linux/of_fdt.h
> +++ b/include/linux/of_fdt.h
> @@ -81,6 +81,7 @@ extern const void *of_flat_dt_match_machine(const void *default_match,
>  /* Other Prototypes */
>  extern void unflatten_device_tree(void);
>  extern void unflatten_and_copy_device_tree(void);
> +extern void setup_of(void);
>  extern void early_init_devtree(void *);
>  extern void early_get_first_memblock_info(void *, phys_addr_t *);
>  #else /* CONFIG_OF_EARLY_FLATTREE */
> @@ -91,6 +92,7 @@ static inline void early_init_fdt_reserve_self(void) {}
>  static inline const char *of_flat_dt_get_machine_name(void) { return NULL; }
>  static inline void unflatten_device_tree(void) {}
>  static inline void unflatten_and_copy_device_tree(void) {}
> +static inline void of_setup(void) {}

Shouldn't this be setup_of(void) ?

-- 
Clément Léger,
Embedded Linux and Kernel engineer at Bootlin
https://bootlin.com