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

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Date:   Tue, 3 Jan 2017 14:11:08 +0200
From:   Pantelis Antoniou <pantelis.antoniou@...sulko.com>
To:     Frank Rowand <frowand.list@...il.com>
Cc:     Heinrich Schuchardt <xypron.glpk@....de>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 0/4 v2] of/overlay: sysfs based ABI for dt overlays

Hi Frank, Heinrich,

> On Dec 22, 2016, at 21:00 , Frank Rowand <frowand.list@...il.com> wrote:
> 
> 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.
> 

I think it would be best if we focus on getting the configfs based loader
to work. It is pretty similar to what Heinrich is proposing.

> -Frank
> 

Regards

— Pantelis

> 
>> 
>> 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