[PATCH 6/8] of: overlay: add FIT overlay support

[Sascha Hauer]

On Fri, Mar 22, 2024 at 05:49:51PM +0100, Marco Felsch wrote:
> This adds the support to load devicetree overlays from an FIT image.
> There are quite a few options to handle FIT overlays since the FIT
> overlay spec is not very strict.
> 
> This patch implement the most configurable case where each overlay does
> have it's own config node (including the optional signature).
> 
> - The "name" filter check is performed on the config-node name (the node
>   under the configurations) and not the FIT overlay image name (the node
>   name under the images node).
> - The "content" filter check does not differ from the file based overlay
>   handling.
> 
> Signed-off-by: Marco Felsch <m.felsch at pengutronix.de>
> ---
>  drivers/of/overlay.c | 110 ++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 103 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
> index e9fd5c0a1f7d..c8e70ab00091 100644
> --- a/drivers/of/overlay.c
> +++ b/drivers/of/overlay.c
> @@ -8,10 +8,12 @@
>   */
>  #define pr_fmt(fmt) "of_overlay: " fmt
>  
> +#include <bootm.h>
>  #include <common.h>
>  #include <of.h>
>  #include <errno.h>
>  #include <globalvar.h>
> +#include <image-fit.h>
>  #include <magicvar.h>
>  #include <string.h>
>  #include <libfile.h>
> @@ -473,9 +475,103 @@ static int of_overlay_global_fixup_dir(struct device_node *root, const char *ovl
>  	return ret;
>  }
>  
> +static int of_overlay_apply_fit(struct device_node *root, struct fit_handle *fit,
> +				struct device_node *config)
> +{
> +	const char *name = config->name;
> +	struct device_node *overlay;
> +	unsigned long ovl_sz;
> +	const void *ovl;
> +	int ret;
> +
> +	if (!fit_has_image(fit, config, "fdt"))
> +		return 0;
> +
> +	if (!of_overlay_matches_filter(name, NULL))
> +		return 0;
> +
> +	ret = fit_open_image(fit, config, "fdt", &ovl, &ovl_sz);
> +	if (ret)
> +		return ret;
> +
> +	overlay = of_unflatten_dtb(ovl, ovl_sz);
> +
> +	if (!of_overlay_matches_filter(NULL, overlay)) {
> +		ret = 0;
> +		goto out;
> +	}
> +
> +	ret = of_overlay_apply_tree(root, overlay);
> +	if (ret == -ENODEV)
> +		pr_debug("Not applied %s (not compatible)\n", name);
> +	else if (ret)
> +		pr_err("Cannot apply %s: %s\n", name, strerror(-ret));
> +	else
> +		pr_info("Applied %s\n", name);
> +
> +out:
> +	of_delete_node(overlay);
> +
> +	return ret;
> +}
> +
> +static int of_overlay_global_fixup_fit(struct device_node *root, const char *ovl_dev)
> +{
> +	enum bootm_verify verify = bootm_get_verify_mode();
> +	struct device_node *conf_node;
> +	struct fit_handle *fit;
> +	struct stat s;
> +	int ret;
> +
> +	if (!IS_ENABLED(CONFIG_FITIMAGE))
> +		return 0;
> +
> +	if (stat(of_overlay_path, &s))
> +		return -errno;

Why this? The caller already checked for existence of of_overlay_path.
Besides, it is not even used in this function.

> +
> +	fit = fit_open(ovl_dev, 0, verify, s.st_size);
> +	if (IS_ERR(fit)) {
> +		pr_err("Loading FIT image %s failed with: %pe\n", ovl_dev, fit);
> +		return PTR_ERR(fit);
> +	}

Are you anticipating taking only the overlays from a FIT image and the
kernel coming from somewhere else? Otherwise I would expect the
integration to happen in the bootm and FIT code where we already have a
handle to the opened FIT image. It seems wasteful to open the same FIT
image here again.

> +
> +	for_each_child_of_node(fit->configurations, conf_node) {
> +		if (!fit_config_is_overlay(conf_node))
> +			continue;
> +
> +		ret = fit_config_verify_signature(fit, conf_node);
> +		if (ret)
> +			goto out;
> +
> +		ret = of_overlay_apply_fit(root, fit, conf_node);
> +		if (ret)
> +			goto out;
> +	}
> +
> +out:
> +	fit_close(fit);
> +	return ret;
> +}
> +
>  static int of_overlay_global_fixup(struct device_node *root, void *data)
>  {
> -	return of_overlay_global_fixup_dir(root, of_overlay_path);
> +	struct stat s;
> +
> +	if (isempty(of_overlay_path))
> +		return 0;
> +
> +	if (stat(of_overlay_path, &s)) {
> +		pr_err("Failed to detect file status\n");
> +		return -errno;
> +	}
> +
> +	if (S_ISDIR(s.st_mode))
> +		return of_overlay_global_fixup_dir(root, of_overlay_path);
> +	else if (S_ISCHR(s.st_mode) || S_ISBLK(s.st_mode))
> +		return of_overlay_global_fixup_fit(root, of_overlay_path);

Why must the FIT image providing overlays be on a plain block device?
Shouldn't we allow FIT images to live in a filesystem?

Anyway, as said I think this is the wrong place to implement this. When
opening a FIT image it's already clear that we should take the overlays
from that image, and not open some image again.

Sascha

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