Merge tag 'gpio-v5.6-1' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-gpio

Pull GPIO updates from Linus Walleij:
 "This is the bulk of GPIO changes for the v5.6 kernel cycle.

  This is a pretty calm cycle so far, nothing special going on really.
  Some more changes will come in from the irqchip and pin control trees.

  I also deleted an orphan include file for FMC that was dangling since
  subsystem was removed.

  Core changes:

   - Document the usecases for the kernelspace vs userspace handling of
     GPIOs.

   - Handle MSI (message signalled interrupts) properly in the core
     hierarchical irqdomain code.

   - Fix a rare race condition while initializing the descriptor array.

  New drivers:

   - Xylon LogiCVC GPIO driver.

   - WDC934x GPIO controller driver.

  Driver improvements:

   - Implemented suspend/resume in the Tegra driver.

   - MPC8xx edge detection fixup.

   - Properly convert ThunderX to use hierarchical irqdomain with
     GPIOLIB_IRQCHIP on top of the revert of the previous buggy
     switchover. This time it works (hopefully).

  Misc:

   - Drop a FMC remnant file <linux/ipmi-fru.h>

   - A slew of fixes"

* tag 'gpio-v5.6-1' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-gpio: (48 commits)
  MAINTAINERS: Replace Tien Hock Loh as Altera PIO maintainer
  gpiolib: hold gpio devices lock until ->descs array is initialised
  gpio: aspeed-sgpio: fixed typos
  gpio: mvebu: clear irq in edge cause register before unmask edge irq
  gpiolib: Lower verbosity when allocating hierarchy irq
  gpiolib: Remove duplicated function gpio_do_set_config()
  gpio: Fix the no return statement warning
  gpio: wcd934x: Add support to wcd934x gpio controller
  gpiolib: remove set but not used variable 'config'
  gpio: vx855: fixed a typo
  gpio: mockup: sort headers alphabetically
  gpio: mockup: update the license tag
  gpio: Remove the unused flags
  gpiolib: Set lockdep class for hierarchical irq domains
  gpio: thunderx: Switch to GPIOLIB_IRQCHIP
  gpiolib: Add the support for the msi parent domain
  gpiolib: Add support for the irqdomain which doesn't use irq_fwspec as arg
  gpio: Add use guidance documentation
  dt-bindings: gpio: wcd934x: Add bindings for gpio
  gpio: altera: change to platform_get_irq_optional to avoid false-positive error
  ...

4 files changed, 57 insertions, 4 deletions

diff --git a/Documentation/driver-api/driver-model/devres.rst b/Documentation/driver-api/driver-model/devres.rst
index 20e07e40be02..46c13780994c 100644
--- a/Documentation/driver-api/driver-model/devres.rst
+++ b/Documentation/driver-api/driver-model/devres.rst
@@ -267,6 +267,8 @@ DRM
 
 GPIO
   devm_gpiod_get()
+  devm_gpiod_get_array()
+  devm_gpiod_get_array_optional()
   devm_gpiod_get_index()
   devm_gpiod_get_index_optional()
   devm_gpiod_get_optional()
diff --git a/Documentation/driver-api/gpio/drivers-on-gpio.rst b/Documentation/driver-api/gpio/drivers-on-gpio.rst
index f3a189320e11..820b403d50f6 100644
--- a/Documentation/driver-api/gpio/drivers-on-gpio.rst
+++ b/Documentation/driver-api/gpio/drivers-on-gpio.rst
@@ -95,7 +95,7 @@ to emulate MCTRL (modem control) signals CTS/RTS by using two GPIO lines. The
 MTD NOR flash has add-ons for extra GPIO lines too, though the address bus is
 usually connected directly to the flash.
 
-Use those instead of talking directly to the GPIOs using sysfs; they integrate
-with kernel frameworks better than your userspace code could. Needless to say,
-just using the appropriate kernel drivers will simplify and speed up your
-embedded hacking in particular by providing ready-made components.
+Use those instead of talking directly to the GPIOs from userspace; they
+integrate with kernel frameworks better than your userspace code could.
+Needless to say, just using the appropriate kernel drivers will simplify and
+speed up your embedded hacking in particular by providing ready-made components.
diff --git a/Documentation/driver-api/gpio/index.rst b/Documentation/driver-api/gpio/index.rst
index 5b61032aa4ea..1d48fe248f05 100644
--- a/Documentation/driver-api/gpio/index.rst
+++ b/Documentation/driver-api/gpio/index.rst
@@ -8,6 +8,7 @@ Contents:
    :maxdepth: 2
 
    intro
+   using-gpio
    driver
    consumer
    board
diff --git a/Documentation/driver-api/gpio/using-gpio.rst b/Documentation/driver-api/gpio/using-gpio.rst
new file mode 100644
index 000000000000..dda069444032
--- /dev/null
+++ b/Documentation/driver-api/gpio/using-gpio.rst
@@ -0,0 +1,50 @@
+=========================
+Using GPIO Lines in Linux
+=========================
+
+The Linux kernel exists to abstract and present hardware to users. GPIO lines
+as such are normally not user facing abstractions. The most obvious, natural
+and preferred way to use GPIO lines is to let kernel hardware drivers deal
+with them.
+
+For examples of already existing generic drivers that will also be good
+examples for any other kernel drivers you want to author, refer to
+:doc:`drivers-on-gpio`
+
+For any kind of mass produced system you want to support, such as servers,
+laptops, phones, tablets, routers, and any consumer or office or business goods
+using appropriate kernel drivers is paramount. Submit your code for inclusion
+in the upstream Linux kernel when you feel it is mature enough and you will get
+help to refine it, see :doc:`../../process/submitting-patches`.
+
+In Linux GPIO lines also have a userspace ABI.
+
+The userspace ABI is intended for one-off deployments. Examples are prototypes,
+factory lines, maker community projects, workshop specimen, production tools,
+industrial automation, PLC-type use cases, door controllers, in short a piece
+of specialized equipment that is not produced by the numbers, requiring
+operators to have a deep knowledge of the equipment and knows about the
+software-hardware interface to be set up. They should not have a natural fit
+to any existing kernel subsystem and not be a good fit for an operating system,
+because of not being reusable or abstract enough, or involving a lot of non
+computer hardware related policy.
+
+Applications that have a good reason to use the industrial I/O (IIO) subsystem
+from userspace will likely be a good fit for using GPIO lines from userspace as
+well.
+
+Do not under any circumstances abuse the GPIO userspace ABI to cut corners in
+any product development projects. If you use it for prototyping, then do not
+productify the prototype: rewrite it using proper kernel drivers. Do not under
+any circumstances deploy any uniform products using GPIO from userspace.
+
+The userspace ABI is a character device for each GPIO hardware unit (GPIO chip).
+These devices will appear on the system as ``/dev/gpiochip0`` thru
+``/dev/gpiochipN``. Examples of how to directly use the userspace ABI can be
+found in the kernel tree ``tools/gpio`` subdirectory.
+
+For structured and managed applications, we recommend that you make use of the
+libgpiod_ library. This provides helper abstractions, command line utlities
+and arbitration for multiple simultaneous consumers on the same GPIO chip.
+
+.. _libgpiod: https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/