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linux-next/Documentation/driver-api/gpio/drivers-on-gpio.rst
Linus Torvalds 3fd14cdcc0 MTD changes:
Core:
     * Remove support for asynchronous erase (not implemented by any of
       the existing drivers anyway)
     * Remove Cyrille from the list of SPI NOR and MTD maintainers
     * Fix kernel doc headers
     * Allow users to define the partitions parsers they want to test
       through a DT property (compatible of the partitions subnode)
     * Remove the bfin-async-flash driver (the only architecture using
       it has been removed)
     * Fix pagetest test
     * Add extra checks in mtd_erase()
     * Simplify the MTD partition creation logic and get rid of
       mtd_add_device_partitions()
 
    Drivers:
     * Add endianness information to the physmap DT binding
     * Add Eon EN29LV400A IDs to JEDEC probe logic
     * Use %*ph where appropriate
 
 SPI NOR changes:
   Drivers:
     * Make fsl-quaspi assign different names to MTD devices connected
       to the same QSPI controller
     * Remove an unneeded driver.bus assigned in the fsl-qspi driver
 
 NAND changes:
   Core:
     * Prepare arrival of the SPI NAND subsystem by implementing a
       generic (interface-agnostic) layer to ease manipulation of NAND
       devices
     * Move onenand code base to the drivers/mtd/nand/ dir
     * Rework timing mode selection
     * Provide a generic way for NAND chip drivers to flag a specific
       GET/SET FEATURE operation as supported/unsupported
     * Stop embedding ONFI/JEDEC param page in nand_chip
 
   Drivers:
     * Rework/cleanup of the mxc driver
     * Various cleanups in the vf610 driver
     * Migrate the fsmc and vf610 to ->exec_op()
     * Get rid of the pxa driver (replaced by marvell_nand)
     * Support ->setup_data_interface() in the GPMI driver
     * Fix probe error path in several drivers
     * Remove support for unused hw_syndrome mode in sunxi_nand
     * Various minor improvements
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Merge tag 'mtd/for-4.17' of git://git.infradead.org/linux-mtd

Pull MTD updates from Boris Brezillon:
 "MTD Core:
   - Remove support for asynchronous erase (not implemented by any of
     the existing drivers anyway)
   - Remove Cyrille from the list of SPI NOR and MTD maintainers
   - Fix kernel doc headers
   - Allow users to define the partitions parsers they want to test
     through a DT property (compatible of the partitions subnode)
   - Remove the bfin-async-flash driver (the only architecture using it
     has been removed)
   - Fix pagetest test
   - Add extra checks in mtd_erase()
   - Simplify the MTD partition creation logic and get rid of
     mtd_add_device_partitions()

  MTD Drivers:
   - Add endianness information to the physmap DT binding
   - Add Eon EN29LV400A IDs to JEDEC probe logic
   - Use %*ph where appropriate

  SPI NOR Drivers:
   - Make fsl-quaspi assign different names to MTD devices connected to
     the same QSPI controller
   - Remove an unneeded driver.bus assigned in the fsl-qspi driver

  NAND Core:
   - Prepare arrival of the SPI NAND subsystem by implementing a generic
     (interface-agnostic) layer to ease manipulation of NAND devices
   - Move onenand code base to the drivers/mtd/nand/ dir
   - Rework timing mode selection
   - Provide a generic way for NAND chip drivers to flag a specific
     GET/SET FEATURE operation as supported/unsupported
   - Stop embedding ONFI/JEDEC param page in nand_chip

  NAND Drivers:
   - Rework/cleanup of the mxc driver
   - Various cleanups in the vf610 driver
   - Migrate the fsmc and vf610 to ->exec_op()
   - Get rid of the pxa driver (replaced by marvell_nand)
   - Support ->setup_data_interface() in the GPMI driver
   - Fix probe error path in several drivers
   - Remove support for unused hw_syndrome mode in sunxi_nand
   - Various minor improvements"

* tag 'mtd/for-4.17' of git://git.infradead.org/linux-mtd: (89 commits)
  dt-bindings: fsl-quadspi: Add the example of two SPI NOR
  mtd: fsl-quadspi: Distinguish the mtd device names
  mtd: nand: Fix some function description mismatches in core.c
  mtd: fsl-quadspi: Remove unneeded driver.bus assignment
  mtd: rawnand: marvell: Rename ->ecc_clk into ->core_clk
  mtd: rawnand: s3c2410: enhance the probe function error path
  mtd: rawnand: tango: fix probe function error path
  mtd: rawnand: sh_flctl: fix the probe function error path
  mtd: rawnand: omap2: fix the probe function error path
  mtd: rawnand: mxc: fix probe function error path
  mtd: rawnand: denali: fix probe function error path
  mtd: rawnand: davinci: fix probe function error path
  mtd: rawnand: cafe: fix probe function error path
  mtd: rawnand: brcmnand: fix probe function error path
  mtd: rawnand: sunxi: Stop supporting ECC_HW_SYNDROME mode
  mtd: rawnand: marvell: Fix clock resource by adding a register clock
  mtd: ftl: Use DIV_ROUND_UP()
  mtd: Fix some function description mismatches in mtdcore.c
  mtd: physmap_of: update struct map_info's swap as per map requirement
  dt-bindings: mtd-physmap: Add endianness supports
  ...
2018-04-06 12:15:41 -07:00

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ReStructuredText

============================
Subsystem drivers using GPIO
============================
Note that standard kernel drivers exist for common GPIO tasks and will provide
the right in-kernel and userspace APIs/ABIs for the job, and that these
drivers can quite easily interconnect with other kernel subsystems using
hardware descriptions such as device tree or ACPI:
- leds-gpio: drivers/leds/leds-gpio.c will handle LEDs connected to GPIO
lines, giving you the LED sysfs interface
- ledtrig-gpio: drivers/leds/trigger/ledtrig-gpio.c will provide a LED trigger,
i.e. a LED will turn on/off in response to a GPIO line going high or low
(and that LED may in turn use the leds-gpio as per above).
- gpio-keys: drivers/input/keyboard/gpio_keys.c is used when your GPIO line
can generate interrupts in response to a key press. Also supports debounce.
- gpio-keys-polled: drivers/input/keyboard/gpio_keys_polled.c is used when your
GPIO line cannot generate interrupts, so it needs to be periodically polled
by a timer.
- gpio_mouse: drivers/input/mouse/gpio_mouse.c is used to provide a mouse with
up to three buttons by simply using GPIOs and no mouse port. You can cut the
mouse cable and connect the wires to GPIO lines or solder a mouse connector
to the lines for a more permanent solution of this type.
- gpio-beeper: drivers/input/misc/gpio-beeper.c is used to provide a beep from
an external speaker connected to a GPIO line.
- extcon-gpio: drivers/extcon/extcon-gpio.c is used when you need to read an
external connector status, such as a headset line for an audio driver or an
HDMI connector. It will provide a better userspace sysfs interface than GPIO.
- restart-gpio: drivers/power/reset/gpio-restart.c is used to restart/reboot
the system by pulling a GPIO line and will register a restart handler so
userspace can issue the right system call to restart the system.
- poweroff-gpio: drivers/power/reset/gpio-poweroff.c is used to power the
system down by pulling a GPIO line and will register a pm_power_off()
callback so that userspace can issue the right system call to power down the
system.
- gpio-gate-clock: drivers/clk/clk-gpio.c is used to control a gated clock
(off/on) that uses a GPIO, and integrated with the clock subsystem.
- i2c-gpio: drivers/i2c/busses/i2c-gpio.c is used to drive an I2C bus
(two wires, SDA and SCL lines) by hammering (bitbang) two GPIO lines. It will
appear as any other I2C bus to the system and makes it possible to connect
drivers for the I2C devices on the bus like any other I2C bus driver.
- spi_gpio: drivers/spi/spi-gpio.c is used to drive an SPI bus (variable number
of wires, at least SCK and optionally MISO, MOSI and chip select lines) using
GPIO hammering (bitbang). It will appear as any other SPI bus on the system
and makes it possible to connect drivers for SPI devices on the bus like
any other SPI bus driver. For example any MMC/SD card can then be connected
to this SPI by using the mmc_spi host from the MMC/SD card subsystem.
- w1-gpio: drivers/w1/masters/w1-gpio.c is used to drive a one-wire bus using
a GPIO line, integrating with the W1 subsystem and handling devices on
the bus like any other W1 device.
- gpio-fan: drivers/hwmon/gpio-fan.c is used to control a fan for cooling the
system, connected to a GPIO line (and optionally a GPIO alarm line),
presenting all the right in-kernel and sysfs interfaces to make your system
not overheat.
- gpio-regulator: drivers/regulator/gpio-regulator.c is used to control a
regulator providing a certain voltage by pulling a GPIO line, integrating
with the regulator subsystem and giving you all the right interfaces.
- gpio-wdt: drivers/watchdog/gpio_wdt.c is used to provide a watchdog timer
that will periodically "ping" a hardware connected to a GPIO line by toggling
it from 1-to-0-to-1. If that hardware does not receive its "ping"
periodically, it will reset the system.
- gpio-nand: drivers/mtd/nand/raw/gpio.c is used to connect a NAND flash chip
to a set of simple GPIO lines: RDY, NCE, ALE, CLE, NWP. It interacts with the
NAND flash MTD subsystem and provides chip access and partition parsing like
any other NAND driving hardware.
- ps2-gpio: drivers/input/serio/ps2-gpio.c is used to drive a PS/2 (IBM) serio
bus, data and clock line, by bit banging two GPIO lines. It will appear as
any other serio bus to the system and makes it possible to connect drivers
for e.g. keyboards and other PS/2 protocol based devices.
Apart from this there are special GPIO drivers in subsystems like MMC/SD to
read card detect and write protect GPIO lines, and in the TTY serial subsystem
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.