• Linus Walleij's avatar
    drivers: create a pin control subsystem · 2744e8af
    Linus Walleij authored
    This creates a subsystem for handling of pin control devices.
    These are devices that control different aspects of package
    pins.
    
    Currently it handles pinmuxing, i.e. assigning electronic
    functions to groups of pins on primarily PGA and BGA type of
    chip packages which are common in embedded systems.
    
    The plan is to also handle other I/O pin control aspects
    such as biasing, driving, input properties such as
    schmitt-triggering, load capacitance etc within this
    subsystem, to remove a lot of ARM arch code as well as
    feature-creepy GPIO drivers which are implementing the same
    thing over and over again.
    
    This is being done to depopulate the arch/arm/* directory
    of such custom drivers and try to abstract the infrastructure
    they all need. See the Documentation/pinctrl.txt file that is
    part of this patch for more details.
    
    ChangeLog v1->v2:
    
    - Various minor fixes from Joe's and Stephens review comments
    - Added a pinmux_config() that can invoke custom configuration
      with arbitrary data passed in or out to/from the pinmux driver
    
    ChangeLog v2->v3:
    
    - Renamed subsystem folder to "pinctrl" since we will likely
      want to keep other pin control such as biasing in this
      subsystem too, so let us keep to something generic even though
      we're mainly doing pinmux now.
    - As a consequence, register pins as an abstract entity separate
      from the pinmux. The muxing functions will claim pins out of the
      pin pool and make sure they do not collide. Pins can now be
      named by the pinctrl core.
    - Converted the pin lookup from a static array into a radix tree,
      I agreed with Grant Likely to try to avoid any static allocation
      (which is crap for device tree stuff) so I just rewrote this
      to be dynamic, just like irq number descriptors. The
      platform-wide definition of number of pins goes away - this is
      now just the sum total of the pins registered to the subsystem.
    - Make sure mappings with only a function name and no device
      works properly.
    
    ChangeLog v3->v4:
    
    - Define a number space per controller instead of globally,
      Stephen and Grant requested the same thing so now maps need to
      define target controller, and the radix tree of pin descriptors
      is a property on each pin controller device.
    - Add a compulsory pinctrl device entry to the pinctrl mapping
      table. This must match the pinctrl device, like "pinctrl.0"
    - Split the file core.c in two: core.c and pinmux.c where the
      latter carry all pinmux stuff, the core is for generic pin
      control, and use local headers to access functionality between
      files. It is now possible to implement a "blank" pin controller
      without pinmux capabilities. This split will make new additions
      like pindrive.c, pinbias.c etc possible for combined drivers
      and chunks of functionality which is a GoodThing(TM).
    - Rewrite the interaction with the GPIO subsystem - the pin
      controller descriptor now handles this by defining an offset
      into the GPIO numberspace for its handled pin range. This is
      used to look up the apropriate pin controller for a GPIO pin.
      Then that specific GPIO range is matched 1-1 for the target
      controller instance.
    - Fixed a number of review comments from Joe Perches.
    - Broke out a header file pinctrl.h for the core pin handling
      stuff that will be reused by other stuff than pinmux.
    - Fixed some erroneous EXPORT() stuff.
    - Remove mispatched U300 Kconfig and Makefile entries
    - Fixed a number of review comments from Stephen Warren, not all
      of them - still WIP. But I think the new mapping that will
      specify which function goes to which pin mux controller address
      50% of your concerns (else beat me up).
    
    ChangeLog v4->v5:
    
    - Defined a "position" for each function, so the pin controller now
      tracks a function in a certain position, and the pinmux maps define
      what position you want the function in. (Feedback from Stephen
      Warren and Sascha Hauer).
    - Since we now need to request a combined function+position from
      the machine mapping table that connect mux settings to drivers,
      it was extended with a position field and a name field. The
      name field is now used if you e.g. need to switch between two
      mux map settings at runtime.
    - Switched from a class device to using struct bus_type for this
      subsystem. Verified sysfs functionality: seems to work fine.
      (Feedback from Arnd Bergmann and Greg Kroah-Hartman)
    - Define a per pincontroller list of GPIO ranges from the GPIO
      pin space that can be handled by the pin controller. These can
      be added one by one at runtime. (Feedback from Barry Song)
    - Expanded documentation of regulator_[get|enable|disable|put]
      semantics.
    - Fixed a number of review comments from Barry Song. (Thanks!)
    
    ChangeLog v5->v6:
    
    - Create an abstract pin group concept that can sort pins into
      named and enumerated groups no matter what the use of these
      groups may be, one possible usecase is a group of pins being
      muxed in or so. The intention is however to also use these
      groups for other pin control activities.
    - Make it compulsory for pinmux functions to associate with
      at least one group, so the abstract pin group concept is used
      to define the groups of pins affected by a pinmux function.
      The pinmux driver interface has been altered so as to enforce
      a function to list applicable groups per function.
    - Provide an optional .group entry in the pinmux machine map
      so the map can select beteween different available groups
      to be used with a certain function.
    - Consequent changes all over the place so that e.g. debugfs
      present reasonable information about the world.
    - Drop the per-pin mux (*config) function in the pinmux_ops
      struct - I was afraid that this would start to be used for
      things totally unrelated to muxing, we can introduce that to
      the generic struct pinctrl_ops if needed. I want to keep
      muxing orthogonal to other pin control subjects and not mix
      these things up.
    
    ChangeLog v6->v7:
    
    - Make it possible to have several map entries matching the
      same device, pin controller and function, but using
      a different group, and alter the semantics so that
      pinmux_get() will pick all matching map entries, and
      store the associated groups in a list. The list will
      then be iterated over at pinmux_enable()/pinmux_disable()
      and corresponding driver functions called for each
      defined group. Notice that you're only allowed to map
      multiple *groups* to the same
      { device, pin controller, function } triplet, attempts
      to map the same device to multiple pin controllers will
      for example fail. This is hopefully the crucial feature
      requested by Stephen Warren.
    - Add a pinmux hogging field to the pinmux mapping entries,
      and enable the pinmux core to hog pinmux map entries.
      This currently only works for pinmuxes without assigned
      devices as it looks now, but with device trees we can
      look up the corresponding struct device * entries when
      we register the pinmux driver, and have it hog each
      pinmux map in turn, for a simple approach to
      non-dynamic pin muxing. This addresses an issue from
      Grant Likely that the machine should take care of as
      much of the pinmux setup as possible, not the devices.
      By supplying a list of hogs, it can now instruct the
      core to take care of any static mappings.
    - Switch pinmux group retrieveal function to grab an
      array of strings representing the groups rather than an
      array of unsigned and rewrite accordingly.
    - Alter debugfs to show the grouplist handled by each
      pinmux. Also add a list of hogs.
    - Dynamically allocate a struct pinmux at pinmux_get() and
      free it at pinmux_put(), then add these to the global
      list of pinmuxes active as we go along.
    - Go over the list of pinmux maps at pinmux_get() time
      and repeatedly apply matches.
    - Retrieve applicable groups per function from the driver
      as a string array rather than a unsigned array, then
      lookup the enumerators.
    - Make the device to pinmux map a singleton - only allow the
      mapping table to be registered once and even tag the
      registration function with __init so it surely won't be
      abused.
    - Create a separate debugfs file to view the pinmux map at
      runtime.
    - Introduce a spin lock to the pin descriptor struct, lock it
      when modifying pin status entries. Reported by Stijn Devriendt.
    - Fix up the documentation after review from Stephen Warren.
    - Let the GPIO ranges give names as const char * instead of some
      fixed-length string.
    - add a function to unregister GPIO ranges to mirror the
      registration function.
    - Privatized the struct pinctrl_device and removed it from the
      <linux/pinctrl/pinctrl.h> API, the drivers do not need to know
      the members of this struct. It is now in the local header
      "core.h".
    - Rename the concept of "anonymous" mux maps to "system" muxes
      and add convenience macros and documentation.
    
    ChangeLog v7->v8:
    
    - Delete the leftover pinmux_config() function from the
     <linux/pinctrl/pinmux.h> header.
    - Fix a race condition found by Stijn Devriendt in pin_request()
    
    ChangeLog v8->v9:
    
    - Drop the bus_type and the sysfs attributes and all, we're not on
      the clear about how this should be used for e.g. userspace
      interfaces so let us save this for the future.
    - Use the right name in MAINTAINERS, PIN CONTROL rather than
      PINMUX
    - Don't kfree() the device state holder, let the .remove() callback
      handle this.
    - Fix up numerous kerneldoc headers to have one line for the function
      description and more verbose documentation below the parameters
    
    ChangeLog v9->v10:
    - pinctrl: EXPORT_SYMBOL needs export.h, folded in a patch
      from Steven Rothwell
    - fix pinctrl_register error handling, folded in a patch from
      Axel Lin
    - Various fixes to documentation text so that it's consistent.
    - Removed pointless comment from drivers/Kconfig
    - Removed dependency on SYSFS since we removed the bus in
      v9.
    - Renamed hopelessly abbreviated pctldev_* functions to the
      more verbose pinctrl_dev_*
    - Drop mutex properly when looking up GPIO ranges
    - Return NULL instead of ERR_PTR() errors on registration of
      pin controllers, using cast pointers is fragile. We can
      live without the detailed error codes for sure.
    
    Cc: Stijn Devriendt <highguy@gmail.com>
    Cc: Joe Perches <joe@perches.com>
    Cc: Russell King <linux@arm.linux.org.uk>
    Acked-by: default avatarGrant Likely <grant.likely@secretlab.ca>
    Acked-by: default avatarStephen Warren <swarren@nvidia.com>
    Tested-by: default avatarBarry Song <21cnbao@gmail.com>
    Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
    2744e8af
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