linux-kernel - Re: [PATCH 0/4 v2] of/overlay: sysfs based ABI for dt overlays

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Date:   Thu, 22 Dec 2016 11:00:11 -0800
From:   Frank Rowand <frowand.list@...il.com>
To:     Heinrich Schuchardt <xypron.glpk@....de>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 0/4 v2] of/overlay: sysfs based ABI for dt overlays

Hi Heinrich,

On 12/20/16 11:04, Heinrich Schuchardt wrote:
> Currently the kernel only supplies an internal API for creating
> and destroying device tree overlays.
> 
> For some boards vendor specific kernel modules exist for
> managing device tree overlays but they have not been
> upstreamed or upstreaming stalled.
> https://lkml.org/lkml/2015/6/12/624
> https://lkml.org/lkml/2013/1/7/366
> 
> This patch series provides a sysfs based ABI for creation and
> destruction of dt overlays in /sys/firmware/devicetree/overlays.
> 
> The following files are provided:
> 
> load:   This is a write only file.
>         A string written to it is interpreted as the path to a
>         flattened device tree overlay file. It is used to create
>         and apply the contained overlays.
> 
> loaded: This is a read only file.
>         It provides the count of loaded overlays as a decimal
>         number.
> 
> unload: This is a write only file.
>         If a positive number n is wrtten to this file the n
>         most recent overlays are destroyed.
>         If a negative number is written to this file all
>         overlays are destroyed.

This patch series follows a _somewhat_ similar approach to what
was first proposed two years ago, and does not address the
issues that were brought up at that time.  See:

  From: Pantelis Antoniou <pantelis.antoniou@...sulko.com>
  Date: Wed,  3 Dec 2014 13:23:28 +0200
  Subject: [PATCH] OF: DT-Overlay configfs interface (v3)

But just responding directly to the two year old issues would not
be a productive approach, since there has been a lot of subsequent
discussion on how to load overlays (you point to two of the many
threads above).  The latest discussions are based on the concept
of describing the overlay attachment points as connectors.

Please join in pushing the connectors discussion along to make
sure that it meets your needs.

-Frank


> 
> Signed-off-by: Heinrich Schuchardt <xypron.glpk@....de>
> 
> version 2:
> 	change sysfs path to
> 	/sys/firmware/devicetree/overlays
> 
> 	Fix errors indicated by kbuild robot:
> 	Add missing inline attribute to of_overlay_count
> 	in patch 1.
> 	Add 'select CONFIG_OF_EARLY_FLATTREE' to Kconfig
> 	in patch 2.
> 
> 	Change unit test cases to check new functions
> 	of_overlay_count and of_overlay_destroy_last.
> 
> Heinrich Schuchardt (4):
>   of/overlay: add API function to count and pop last
>   of/overlay: sysfs based ABI for dt overlays
>   of/overlay: documentation for sysfs ABI 
>   of/overlay: test count and destroy_last
> 
>  .../ABI/testing/sysfs-firmware-devicetree-overlays |  24 +++ 
>  Documentation/devicetree/overlay-notes.txt         |   7 +-
>  drivers/of/Kconfig                                 |  15 ++
>  drivers/of/Makefile                                |   2 + 
>  drivers/of/base.c                                  |   1 + 
>  drivers/of/ov_sysfs.c                              | 223 +++++++++++++++++++++
>  drivers/of/overlay.c                               |  50 +++++
>  drivers/of/unittest.c                              |  15 +-
>  include/linux/of.h                                 |  12 ++
>  9 files changed, 346 insertions(+), 3 deletions(-)
>  create mode 100644 Documentation/ABI/testing/sysfs-firmware-devicetree-overlays
>  create mode 100644 drivers/of/ov_sysfs.c
>