linux-kernel - [RFC v2 0/4] i2c/of: switch I2C IP cores at runtime via OF

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Date:	Wed,  6 Jan 2016 14:51:21 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	linux-i2c@...r.kernel.org
Cc:	Wolfram Sang <wsa@...-dreams.de>, linux-sh@...r.kernel.org,
	Magnus Damm <magnus.damm@...il.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
	Jan Luebbe <jlu@...gutronix.de>
Subject: [RFC v2 0/4] i2c/of: switch I2C IP cores at runtime via OF_DYNAMIC

I know this is gonna be a controversial series, but we have a usecase for this :)

This series allows an I2C bus to switch between multiple masters, i.e. a
n-to-1-demuxer. This is not hot-switching because connected I2C slaves will be
re-instantiated. It is meant to select the best I2C core at runtime once the
task is known. Example: Prefer i2c-gpio over another I2C core because of HW
errata affecting your current runtime configuration.

It works by using OF_DYNAMIC and en-/disabling the i2c parent as needed. See
the binding docs for more details. Because this is largely using OF_DYNAMIC, I
decided to post the whole series to the dt list.

Changes since RFC v1:

* gracefully handle if i2c adapters are not present at runtime
  (driver not loaded yet)
* added more documentation and examples
* properly put the i2c adapters after use
* respect PAGE_SIZE in sysfs_show

This has been tested on a Renesas Lager board switching between i2c-gpio and
two different IP cores (i2c-rcar and i2c-sh_mobile). The rebinding seems to be
working as expected. However, in practice, I couldn't use the HDMI i2c slaves
with another controller yet, because the rcar-du driver OOPSes when unbinding.
This seems unrelated to this series because it can also be triggered via
sysfs-unbind. soc-camera also had problems properly cleaning up on unbind, a
patch for this already has been sent. So, this series is for sure a good test
for the unbind path of drivers.

Let me know what you think.

Thanks,

   Wolfram

Wolfram Sang (4):
  of: make of_mutex public
  dt-bindings: i2c: mux: demux-pinctrl: add bindings
  i2c: mux: demux-pinctrl: add driver
  ARM: shmobile: r8a7790: rework dts to use i2c demuxer

 .../devicetree/bindings/i2c/i2c-demux-pinctrl.txt  | 155 ++++++++++++
 arch/arm/boot/dts/r8a7790-lager.dts                | 141 +++++++----
 drivers/i2c/muxes/Kconfig                          |   9 +
 drivers/i2c/muxes/Makefile                         |   2 +
 drivers/i2c/muxes/i2c-demux-pinctrl.c              | 276 +++++++++++++++++++++
 drivers/of/of_private.h                            |   1 -
 include/linux/of.h                                 |   2 +
 7 files changed, 532 insertions(+), 54 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/i2c/i2c-demux-pinctrl.txt
 create mode 100644 drivers/i2c/muxes/i2c-demux-pinctrl.c

-- 
2.1.4

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