Re: [PATCH v6 0/9] mux controller abstraction and iio/i2c muxes

[Jonathan Cameron]

On 30/11/16 08:16, Peter Rosin wrote:
> Hi!
Just a quick note to encourage people to take a look at this series
if they have the time (I can't talk as it took me almost exactly a
month to take a proper look).

It actually ended up a good deal simpler than I expected so I'm falling
on the side of this making sense rather than pushing all mux complexity
into a 'card driver'.  Covers a lot of cases without a proliferation of
code which is nice.

One addition that may make sense is to provide hooks to allow 'card
drivers' where they are needed. I can certainly conceive of devices
where the complexity does rise to the point where they make sense.
However, we can add them when needed.

Peter, don't give up on this set just yet!

Happy New Year,

Jonathan
> 
> v5 -> v6 changes
> - fix stupidity in mux_chip_priv, mux_gpio_remove and adg792a_remove.
> - change the devicetree bindings for the iio-mux to use a list of strings
>   (channels property) instead of a list children.
> 
> v4 -> v5 changes
> - remove support for fancier dt layouts and go back to the phandle
>   approach from v2 and before, killing the horrible non-working
>   refcounting crap from v4 and avoiding a bunch of life-time issues
>   in v3.
> - introduce the concept of a mux-chip, that can hold one or more
>   mux-controllers (inspired by the pwm subsystem).
> - add dt #mux-control-cells property needed to get to the desired
>   mux controller if a mux chip provides more than one.
> - take away the option to build the mux-core as a module.
> - if the mux controller has an idle state, make sure the mux controller
>   is set up in the idle state initially (when it should be idle).
> - do not use a variable length array on the stack in mux_gpio_set to
>   temporarily store the gpio state, preallocate space instead.
> - fix resource leak on one failure path in mux_gpio_probe.
> - driver for Analog Devices ADG792A/G, literally the first mux chip
>   I found on the Internet with an i2c interface (that was not a
>   dedicated i2c multiplexer like PCA9547) which I used to verify
>   that the abstractions in the mux core are up to the task. Untested,
>   just proof of concept that at least looks pretty and compiles...
> - various touch-ups.
> 
> v3 -> v4 changes
> - rebased onto next-20161122 (depends on recent _available iio changes).
> - added support for having the mux-controller in a child node of a
>   mux-consumer if it is a sole consumer, to hopefully even further satisfy
>   the complaint from Rob (and later Lars-Peter) about dt complexity.
> - the above came at the cost of some rather horrible refcounting code,
>   please review and suggest how it should be done...
> - changed to register a device class instead of a bus.
> - pass in the parent device into mux_control_alloc and require less
>   work from mux-control drivers.
> - changed device names from mux:control%d to mux%d
> - move kernel-doc from mux-core.c to mux.h (and add some bits).
> - give the gpio driver a chance to update all mux pins at once.
> - factor out iio ext_info lookup into new helper function. /Lars-Peter
> - use an unsigned type for the iio ext_info count. /Lars-Peter
> - unified "brag strings" in the file headers.
> 
> v2 -> v3 changes
> - have the mux-controller in the parent node of any mux-controller consumer,
>   to hopefully satisfy complaint from Rob about dt complexity.
> - improve commit message of the mux subsystem commit, making it more
>   general, as requested by Jonathan.
> - remove priv member from struct mux_control and calculate it on the
>   fly. /Jonathan
> - make the function comments in mux-core.c kernel doc. /Jonathan
> - add devm_mux_control_* to Documentation/driver.model/devres.txt. /Jonathan
> - add common dt bindings for mux-controllers, refer to them from the
>   mux-gpio bindings. /Rob
> - clarify how the gpio pins map to the mux state. /Rob
> - separate CONFIG_ variables for the mux core and the mux gpio driver.
> - improve Kconfig help texts.
> - make CONFIG_MUX_GPIO depend on CONFIG_GPIOLIB.
> - keep track of the number of mux states in the mux core.
> - since the iio channel number is used as mux state, it was possible
>   to drop the state member from the mux_child struct.
> - cleanup dt bindings for i2c-mux-simple, it had some of copy-paste
>   problems from ots origin (i2c-mux-gpio).
> - select the mux control subsystem in config for the i2c-mux-simple driver.
> - add entries to MAINTAINERS and my sign-off, I'm now satisfied and know
>   nothing in this to be ashamed of.
> 
> v1 -> v2 changes
> - fixup export of mux_control_put reported by kbuild
> - drop devicetree iio-ext-info property as noted by Lars-Peter,
>   and replace the functionality by exposing all ext_info
>   attributes of the parent channel for each of the muxed
>   channels. A cache on top of that and each muxed channel
>   gets its own view of the ext_info of the parent channel.
> - implement idle-state for muxes
> - clear out the cache on failure in order to force a mux
>   update on the following use
> - cleanup the probe of i2c-mux-simple driver
> - fix a bug in the i2c-mux-simple driver, where failure in
>   the selection of the mux caused a deadlock when the mux
>   was later unconditionally deselected.
> 
> I have a piece of hardware that is using the same 3 GPIO pins
> to control four 8-way muxes. Three of them control ADC lines
> to an ADS1015 chip with an iio driver, and the last one
> controls the SDA line of an i2c bus. We have some deployed
> code to handle this, but you do not want to see it or ever
> hear about it. I'm not sure why I even mention it. Anyway,
> the situation has nagged me to no end for quite some time.
> 
> So, after first getting more intimate with the i2c muxing code
> and later discovering the drivers/iio/inkern.c file and
> writing a couple of drivers making use of it, I came up with
> what I think is an acceptable solution; add a generic mux
> controller driver (and subsystem) that is shared between all
> instances, and combine that with an iio mux driver and a new
> generic i2c mux driver. The new i2c mux I called "simple"
> since it is only hooking the i2c muxing and the new mux
> controller (much like the alsa simple card driver does for ASoC).
> 
> One thing that I would like to do, but don't see a solution
> for, is to move the mux control code that is present in
> various drivers in drivers/i2c/muxes to this new minimalistic
> muxing subsystem, thus converting all present i2c muxes (but
> perhaps not gates and arbitrators) to be i2c-mux-simple muxes.
> 
> I'm using an rwsem to lock a mux, but that isn't really a
> perfect fit. Is there a better locking primitive that I don't
> know about that fits better? I had a mutex at one point, but
> that didn't allow any concurrent accesses at all. At least
> the rwsem allows concurrent access as long as all users
> agree on the mux state, but I suspect that the rwsem will
> degrade to the mutex situation pretty quickly if there is
> any contention.
> 
> Also, the "mux" name feels a bit ambitious, there are many muxes
> in the world, and this tiny bit of code is probably not good
> enough to be a nice fit for all...
> 
> Cheers,
> Peter
> 
> Peter Rosin (9):
>   dt-bindings: document devicetree bindings for mux-controllers and
>     mux-gpio
>   misc: minimal mux subsystem and gpio-based mux controller
>   iio: inkern: api for manipulating ext_info of iio channels
>   dt-bindings: iio: iio-mux: document iio-mux bindings
>   iio: multiplexer: new iio category and iio-mux driver
>   dt-bindings: i2c: i2c-mux-simple: document i2c-mux-simple bindings
>   i2c: i2c-mux-simple: new driver
>   dt-bindings: mux-adg792a: document devicetree bindings for ADG792A/G
>     mux
>   misc: mux-adg792a: add mux controller driver for ADG792A/G
> 
>  .../devicetree/bindings/i2c/i2c-mux-simple.txt     |  81 ++++
>  .../bindings/iio/multiplexer/iio-mux.txt           |  40 ++
>  .../devicetree/bindings/misc/mux-adg792a.txt       |  64 +++
>  .../devicetree/bindings/misc/mux-controller.txt    | 127 ++++++
>  .../devicetree/bindings/misc/mux-gpio.txt          |  68 +++
>  Documentation/driver-model/devres.txt              |   6 +-
>  MAINTAINERS                                        |  14 +
>  drivers/i2c/muxes/Kconfig                          |  13 +
>  drivers/i2c/muxes/Makefile                         |   1 +
>  drivers/i2c/muxes/i2c-mux-simple.c                 | 179 ++++++++
>  drivers/iio/Kconfig                                |   1 +
>  drivers/iio/Makefile                               |   1 +
>  drivers/iio/inkern.c                               |  60 +++
>  drivers/iio/multiplexer/Kconfig                    |  18 +
>  drivers/iio/multiplexer/Makefile                   |   6 +
>  drivers/iio/multiplexer/iio-mux.c                  | 456 +++++++++++++++++++++
>  drivers/misc/Kconfig                               |  42 ++
>  drivers/misc/Makefile                              |   3 +
>  drivers/misc/mux-adg792a.c                         | 154 +++++++
>  drivers/misc/mux-core.c                            | 311 ++++++++++++++
>  drivers/misc/mux-gpio.c                            | 138 +++++++
>  include/linux/iio/consumer.h                       |  37 ++
>  include/linux/mux.h                                | 197 +++++++++
>  23 files changed, 2016 insertions(+), 1 deletion(-)
>  create mode 100644 Documentation/devicetree/bindings/i2c/i2c-mux-simple.txt
>  create mode 100644 Documentation/devicetree/bindings/iio/multiplexer/iio-mux.txt
>  create mode 100644 Documentation/devicetree/bindings/misc/mux-adg792a.txt
>  create mode 100644 Documentation/devicetree/bindings/misc/mux-controller.txt
>  create mode 100644 Documentation/devicetree/bindings/misc/mux-gpio.txt
>  create mode 100644 drivers/i2c/muxes/i2c-mux-simple.c
>  create mode 100644 drivers/iio/multiplexer/Kconfig
>  create mode 100644 drivers/iio/multiplexer/Makefile
>  create mode 100644 drivers/iio/multiplexer/iio-mux.c
>  create mode 100644 drivers/misc/mux-adg792a.c
>  create mode 100644 drivers/misc/mux-core.c
>  create mode 100644 drivers/misc/mux-gpio.c
>  create mode 100644 include/linux/mux.h
>