[PATCH 5/9] boot: add imagemap on-demand loading from storage

[Tom Rini]

On Sun, Aug 23, 2026 at 08:13:55PM +0100, Daniel Golle wrote:
> Introduce imagemap, a small layer that reads image data from a storage
> device on demand and keeps a translation table of the byte ranges
> already loaded into RAM, instead of copying the whole image up front.
> 
> An imagemap device (UCLASS_IMAGEMAP) is created over a partition of a
> block device with imagemap_create(); imagemap_map() then returns a RAM
> pointer for any byte range, reading it in on first access and reusing
> it on later accesses -- so a header probe, verification and the final
> load of the same range share a single read. Block devices cover more
> than raw disks: an MTD partition is reached through mtdblock and a UBI
> volume through ubiblock, each exposed as a named block-device
> partition, so imagemap needs no storage-specific code of its own.
> 
> The read path is built on the SPL struct spl_load_info abstraction and
> a new spl_load_region() helper (added to spl.h): the block reader
> reports the device block length and spl_load_region() performs the
> native sector alignment. imagemap_map_to() keeps a payload byte-exact
> at a caller's load address, reading the aligned middle straight to the
> destination and bouncing only the partial head/tail block.
> 
> Regions that are not placed at a caller-supplied address are allocated
> through the LMB allocator and released on cleanup; the translation
> table doubles as the registry of those allocations. imagemap is gated
> to the full-U-Boot phase, so SPL and TPL carry no new cost.
> 
> Signed-off-by: Daniel Golle <daniel at makrotopia.org>
> ---
[snip]
> diff --git a/include/spl.h b/include/spl.h
> index 5078d7525ab..24df44d23e1 100644
> --- a/include/spl.h
> +++ b/include/spl.h
> @@ -350,10 +350,21 @@ typedef ulong (*spl_load_reader)(struct spl_load_info *load, ulong sector,
>   * @phase: Image phase to load
>   * @no_fdt_update: true to update the FDT with any loadables that are loaded
>   */
> +/*
> + * struct spl_load_info carries a device block length for the SPL block
> + * loaders (CONFIG_SPL_LOAD_BLOCK) and, in full U-Boot, for the imagemap
> + * on-demand loader (CONFIG_IMAGEMAP);

This part should be made clear in updates to the existing comment block.

> imagemap is gated out of the xpl
> + * phases so SPL and TPL carry no new cost.

This doesn't need to be noted I think because..

> + */
> +#if IS_ENABLED(CONFIG_SPL_LOAD_BLOCK) || \
> +	(IS_ENABLED(CONFIG_IMAGEMAP) && !defined(CONFIG_XPL_BUILD))
> +#define SPL_LOAD_INFO_HAS_BL_LEN
> +#endif
> +
>  struct spl_load_info {
>  	spl_load_reader read;
>  	void *priv;
> -#if IS_ENABLED(CONFIG_SPL_LOAD_BLOCK)
> +#ifdef SPL_LOAD_INFO_HAS_BL_LEN

Why not just:
#if IS_ENABLED(CONFIG_SPL_LOAD_BLOCK) || CONFIG_IS_ENABLED(IMAGEMAP)

? Then for when someone says "Ah, I want to do all of this right in SPL"
there's less changes.

-- 
Tom
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