[PATCH v3 0/3] mtd concat device driver

[Bernhard Frauendienst]

Hi everybody,

my router firmware concatenates two identical flash chips into a single
mtd using mtd_concat_create(), and sets up partitions in a way where one
of them crosses the chip boundary. When porting OpenWRT support for the
board from a mach-file based setup to a device-tree based one, I found
that there is no generic way to create a mtd_concat device from within
the dts. The following patches attempt to provide that possibility.

This is a third roll of that patch series, the first one can be seen at
[1]. The second one [2] was a blunder of my own making. Apologies for
not being able to address the correct recipients two times in a row.

In the first discussion, concerns were raised that a driver for a
"virtual" device like this might have no place in the device tree
system. However, I would argue that specifying a composite device is
very similar to specifying the partitions of a mtd, which can also done
in the device tree. In fact, I believe this is the only way to be able
to specify the partitions of such a concat device in the dts file (but
I'm happy to be corrected if I'm mistaken).
I have made the example in the dt-binding documentation a bit more
expressive in this detail.

In the second roll I have also addressed all issues that reviewers have
brought up so far, hopefully to their satisfaction. These were mainly
whitespace fixes and improved comments.

Best regards,
Bernhard

[1] http://lists.infradead.org/pipermail/linux-mtd/2018-September/083832.html
[2] https://lkml.org/lkml/2018/9/7/1015

Bernhard Frauendienst (3):
  mtd: core: add get_mtd_device_by_node
  dt-bindings: add bindings for mtd-concat devices
  mtd: mtdconcat: add dt driver for concat devices

 .../devicetree/bindings/mtd/mtd-concat.txt    |  36 +++++
 drivers/mtd/Kconfig                           |   2 +
 drivers/mtd/Makefile                          |   3 +
 drivers/mtd/composite/Kconfig                 |  12 ++
 drivers/mtd/composite/Makefile                |   6 +
 drivers/mtd/composite/virt_concat.c           | 128 ++++++++++++++++++
 drivers/mtd/mtdcore.c                         |  38 ++++++
 include/linux/mtd/mtd.h                       |   2 +
 8 files changed, 228 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mtd/mtd-concat.txt
 create mode 100644 drivers/mtd/composite/Kconfig
 create mode 100644 drivers/mtd/composite/Makefile
 create mode 100644 drivers/mtd/composite/virt_concat.c

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2.18.0