Re: [PATCH v3 06/10] of: overlay: add FIT overlay support

[Sascha Hauer <s.hauer@pengutronix.de>]

On Tue, Aug 05, 2025 at 10:34:35PM +0200, Marco Felsch wrote:
> On 24-07-15, Sascha Hauer wrote:
> > On Mon, Jul 15, 2024 at 01:30:00PM +0200, Marco Felsch wrote:
> > > Hi Sascha,
> > > 
> > > On 24-07-15, Sascha Hauer wrote:
> > > > On Wed, Jul 03, 2024 at 06:58:34PM +0200, 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@pengutronix.de>
> > > > > ---
> > > > >  drivers/of/overlay.c | 131 ++++++++++++++++++++++++++++++++++++++++++++++++---
> > > > >  1 file changed, 124 insertions(+), 7 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
> > > > > index 5617f322ddca..a980e7aa5e02 100644
> > > > > --- a/drivers/of/overlay.c
> > > > > +++ b/drivers/of/overlay.c
> > > > > @@ -8,10 +8,13 @@
> > > > >   */
> > > > >  #define pr_fmt(fmt) "of_overlay: " fmt
> > > > >  
> > > > > +#include <bootm.h>
> > > > >  #include <common.h>
> > > > >  #include <of.h>
> > > > >  #include <errno.h>
> > > > > +#include <filetype.h>
> > > > >  #include <globalvar.h>
> > > > > +#include <image-fit.h>
> > > > >  #include <magicvar.h>
> > > > >  #include <string.h>
> > > > >  #include <libfile.h>
> > > > > @@ -470,9 +473,123 @@ 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 (!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 bool of_overlay_valid_config(struct fit_handle *fit,
> > > > > +				    struct device_node *config)
> > > > > +{
> > > > > +	/*
> > > > > +	 * Either kernel or firmware is marked as mandatory by U-Boot
> > > > > +	 * (doc/usage/fit/source_file_format.rst) except for overlays
> > > > > +	 * (doc/usage/fit/overlay-fdt-boot.rst). Therefore we need to ensure
> > > > > +	 * that only "fdt" config nodes are recognized as overlay config node.
> > > > > +	 */
> > > > > +	if (!fit_has_image(fit, config, "fdt") ||
> > > > > +	    fit_has_image(fit, config, "kernel") ||
> > > > > +	    fit_has_image(fit, config, "firmware"))
> > > > > +		return false;
> > > > > +
> > > > > +	return true;
> > > > > +}
> > > > > +
> > > > > +static int of_overlay_global_fixup_fit(struct device_node *root,
> > > > > +				       const char *fit_path, loff_t fit_size)
> > > > > +{
> > > > > +	enum bootm_verify verify = bootm_get_verify_mode();
> > > > > +	struct device_node *conf_node;
> > > > > +	struct fit_handle *fit;
> > > > > +	int ret;
> > > > > +
> > > > > +	if (!IS_ENABLED(CONFIG_FITIMAGE))
> > > > > +		return 0;
> > > > 
> > > > The user has explicitly passed a FIT image, but we don't have FIT
> > > > support compiled in. Shouldn't this be an error?
> > > 
> > > Yes you're right. I will return the error and an error-message.
> > > 
> > > > > +	fit = fit_open(fit_path, 0, verify, fit_size);
> > > > > +	if (IS_ERR(fit)) {
> > > > > +		pr_err("Loading FIT image %s failed with: %pe\n", fit_path, fit);
> > > > > +		return PTR_ERR(fit);
> > > > > +	}
> > > > > +
> > > > > +	for_each_child_of_node(fit->configurations, conf_node) {
> > > > > +		if (!of_overlay_valid_config(fit, 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);
> > > > > +	enum filetype type;
> > > > > +	struct stat s;
> > > > > +	int ret;
> > > > > +
> > > > > +	if (isempty(of_overlay_path))
> > > > > +		return 0;
> > > > > +
> > > > > +	if (stat(of_overlay_path, &s)) {
> > > > > +		pr_err("Failed to detect file status\n");
> > > > 
> > > > Maybe something like:
> > > > 
> > > > 	pr_err("Cannot stat global.of.overlay.path (%s): %pe\n", of_overlay_path, ERR_PTR(ret));
> > > > 
> > > > To give the user a better clue what to do about this error?
> > > 
> > > ACK
> > > 
> > > > > +		return -errno;
> > > > > +	}
> > > > > +
> > > > > +	if (S_ISDIR(s.st_mode))
> > > > > +		return of_overlay_global_fixup_dir(root, of_overlay_path);
> > > > > +
> > > > > +	ret = file_name_detect_type(of_overlay_path, &type);
> > > > > +	if (ret)
> > > > > +		return ret;
> > > > > +
> > > > > +	if (type == filetype_oftree)
> > > > > +		return of_overlay_global_fixup_fit(root, of_overlay_path,
> > > > > +						   s.st_size);
> > > > > +
> > > > > +	pr_err("No suitable overlay provider found!\n");
> > > > 
> > > > What other file types are you anticipating here? I would rather assume a
> > > > "... is not a FIT image" message to give the user a clue what is
> > > > expected here.
> > > 
> > > E.g. overlays supplied via an unified kernel image (UKI) which of course
> > > is not supported by barebox yet. Also if we reach this error it means
> > > that the of_overlay_path was neither a DIR nor a FIT therefore I went
> > > the generic way.
> > > 
> > > > I think you could also just drop the filetype detection here and just
> > > > call of_overlay_global_fixup_fit() unconditionally. The resulting
> > > > "Loading FIT image %s failed with: %pe\n" message when a non FIT image
> > > > is to be opened should be enough information for the user.
> > > 
> > > You're right. I took an very defensive approach. We can extend this
> > > later as well if we're going to support UKIs in the future.
> > > 
> > > > Note that it's a bit unfortunate that both a FIT image and a dtbo file
> > > > are detected as device tree files. With the prvious naming
> > > > "global.of.overlay.dir" it was clear that a directory was expected here.
> > > > The "global.of.overlay.path" naming might confuse the user into thinking
> > > > that a path to a dtbo file could be passed here which would then be
> > > > opened as a FIT image. Would be nice to give a meaningful error message
> > > > when a user falls into this trap.
> > > 
> > > Sorry I don't get this. With "global.of.overlay.path" there are now two
> > > possibilities:
> > >  1) It's a directory: in that case the already existing
> > >     of_overlay_global_fixup_dir() is triggered.
> > >  2) It's a file: in that case we try to apply the new fit-overlay
> > >     handling.
> > 
> > In the end global.of.overlay.path specifies where to find device tree
> > overlay files, usually dtbos. If that variable specifies a directory
> > then in this directory indeed dtbos are expected. If the variable
> > specifies a file, then a FIT image is expected and a dtbo doesn't work.
> > This is inconsistent and it might be worth having a message printed
> > when global.of.overlay.path points to a dtbo.
> 
> Sorry, I should have read your comment more carefully, I got it now. Yes
> this is a bit unfortunate. What about:
> 
> BAREBOX_MAGICVAR(global.of.overlay.provider, "Select one overlay provider: directory (default), fit");

How about just accepting either a FIT image or a dtbo if
global.of.overlay.path refers to a file?

Sascha

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