Re: [RFC PATCH 08/20] boot: image-loader: add UBI volume backend

[Daniel Golle <daniel@makrotopia.org>]

On Mon, Feb 23, 2026 at 10:51:09AM -0700, Simon Glass wrote:
> Hi Daniel,
> 
> On Thu, 19 Feb 2026 at 09:51, Daniel Golle <daniel@makrotopia.org> wrote:
> >
> > On Thu, Feb 19, 2026 at 06:09:27AM -0700, Simon Glass wrote:
> > > Hi Daniel,
> > >
> > > On Mon, 16 Feb 2026 at 14:22, Daniel Golle <daniel@makrotopia.org> wrote:
> > > >
> > > > Add a UBI volume storage backend for the image_loader framework.
> > > >
> > > > image_loader_init_ubi() takes a volume name, ensures the UBI device
> > > > is attached (auto-attaching if needed), and installs a .read() callback
> > > > wrapping ubi_volume_read().
> > > >
> > > > Auto-attach works by scanning the device tree for the first MTD
> > > > partition with compatible = "linux,ubi", then calling ubi_part() on
> > > > that partition. The partition name is resolved using the same
> > > > precedence as the MTD partition parser: the "label" property first,
> > > > then "name", then the node name. Since U-Boot only supports a single
> > > > attached UBI device at a time, only the first matching partition is
> > > > used. If a UBI device is already attached, the auto-attach step is
> > > > skipped.
> > > >
> > > > UBI handles bad-block management and wear leveling internally, so the
> > > > read callback is a straightforward passthrough. Note that
> > > > ubi_volume_read() returns positive errno values; the wrapper negates
> > > > them for the image_loader convention.
> > > >
> > > > Gated by CONFIG_IMAGE_LOADER_UBI (depends on CMD_UBI && IMAGE_LOADER).
> > > >
> > > > Signed-off-by: Daniel Golle <daniel@makrotopia.org>
> > > > ---
> > > >  boot/Kconfig            |   8 +++
> > > >  boot/Makefile           |   1 +
> > > >  boot/image-loader-ubi.c | 112 ++++++++++++++++++++++++++++++++++++++++
> > > >  include/image-loader.h  |  13 +++++
> > > >  4 files changed, 134 insertions(+)
> > > >  create mode 100644 boot/image-loader-ubi.c
> > > >
> > > > diff --git a/boot/Kconfig b/boot/Kconfig
> > > > index 23848a0f57e..89832014af6 100644
> > > > --- a/boot/Kconfig
> > > > +++ b/boot/Kconfig
> > > > @@ -1203,6 +1203,14 @@ config IMAGE_LOADER_MTD
> > > >           parallel NAND, etc.) using the image_loader framework.
> > > >           NAND bad blocks are skipped transparently.
> > > >
> > > > +config IMAGE_LOADER_UBI
> > > > +       bool "UBI volume backend for image loader"
> > > > +       depends on IMAGE_LOADER && CMD_UBI
> > > > +       help
> > > > +         Allows loading images from UBI volumes using the image_loader
> > > > +         framework. Auto-attaches the UBI device from the device tree
> > > > +         if not already attached.
> > > > +
> > > >  config DISTRO_DEFAULTS
> > > >         bool "(deprecated) Script-based booting of Linux distributions"
> > > >         select CMDLINE
> > > > diff --git a/boot/Makefile b/boot/Makefile
> > > > index 1dde16db694..7d1d4a28106 100644
> > > > --- a/boot/Makefile
> > > > +++ b/boot/Makefile
> > > > @@ -76,6 +76,7 @@ obj-$(CONFIG_$(PHASE_)BOOTMETH_ANDROID) += bootmeth_android.o
> > > >  obj-$(CONFIG_IMAGE_LOADER) += image-loader.o
> > > >  obj-$(CONFIG_IMAGE_LOADER_BLK) += image-loader-blk.o
> > > >  obj-$(CONFIG_IMAGE_LOADER_MTD) += image-loader-mtd.o
> > > > +obj-$(CONFIG_IMAGE_LOADER_UBI) += image-loader-ubi.o
> > > >
> > > >  obj-$(CONFIG_$(PHASE_)BOOTMETH_VBE_ABREC) += vbe_abrec.o vbe_common.o
> > > >  obj-$(CONFIG_$(PHASE_)BOOTMETH_VBE_ABREC_FW) += vbe_abrec_fw.o
> > > > diff --git a/boot/image-loader-ubi.c b/boot/image-loader-ubi.c
> > > > new file mode 100644
> > > > index 00000000000..64901a13378
> > > > --- /dev/null
> > > > +++ b/boot/image-loader-ubi.c
> > > > @@ -0,0 +1,112 @@
> > > > +// SPDX-License-Identifier: GPL-2.0+
> > > > +/*
> > > > + * UBI volume backend for image_loader
> > > > + *
> > > > + * Copyright (C) 2026 Daniel Golle <daniel@makrotopia.org>
> > > > + */
> > > > +
> > > > +#include <dm/ofnode.h>
> > > > +#include <image-loader.h>
> > > > +#include <log.h>
> > > > +#include <malloc.h>
> > > > +#include <mtd.h>
> > > > +#include <ubi_uboot.h>
> > > > +
> > > > +struct image_loader_ubi_priv {
> > > > +       char *vol_name;
> > > > +};
> > > > +
> > > > +/**
> > > > + * ubi_auto_attach() - attach UBI if not already attached
> > > > + *
> > > > + * If no UBI device is currently attached, walk the device tree for the
> > > > + * first MTD partition node with compatible = "linux,ubi", find the
> > > > + * corresponding MTD device by matching flash_node, and attach UBI to
> > > > + * it via ubi_part_from_mtd().
> > > > + *
> > > > + * Since U-Boot only supports a single attached UBI device at a time,
> > > > + * only the first matching partition is used.
> > > > + *
> > > > + * Return: 0 on success or if already attached, negative errno on failure
> > > > + */
> > > > +static int ubi_auto_attach(void)
> > > > +{
> > > > +       struct mtd_info *mtd;
> > > > +       ofnode node;
> > > > +
> > > > +       /* Already attached? */
> > > > +       if (ubi_devices[0])
> > > > +               return 0;
> > > > +
> > > > +       mtd_probe_devices();
> > >
> > > This should be handled by your new ubi driver for your uclass.
> > >
> > > > +
> > > > +       ofnode_for_each_compatible_node(node, "linux,ubi") {
> > > > +               mtd_for_each_device(mtd) {
> > > > +                       if (ofnode_equal(mtd->flash_node, node))
> > > > +                               goto found;
> > > > +               }
> > > > +       }
> > >
> > > Eek this is really strange. There should be a device so you can use
> > > uclass_first_device(UCLASS_...).
> >
> > I carefully considered turning UBI devices into a UCLASS, but it would
> > be a huge major rewrite of how UBI works in U-Boot, and while that would
> > be a good thing to do, I consider far beyond the scope of supporting a
> > boot method for OpenWrt.
> 
> Oh, I just assumed it supports driver model. But surely it must have a
> UCLASS_BLK device?

Sadly no. Neither UBI devices nor UBI volumes are block storage devices.

Every UBI device does have a UCLASS_MTD parent device, but that
obviously also doesn't uniquely identify the partition on the flash chip
which is used as UBI device -- there can be (and sometimes are, for
dual-boot/redundancy reasons) multiple UBI devices in different
partitions on the same flash.

What I ended up doing now is to move more of the UBI detection and
enumeration logic into ubi_bootdev.c and have imagemap-ubi.c rely
on getting the MTD device and partition index from there.

> 
> >
> > Or did you mean the to-be-create UCLASS_IMAGE_MAPPER?
> 
> No I was talking about ubi.
> 
> Regards,
> Simon