mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-22 08:49:45 +00:00
![Krzysztof Kozlowski](/assets/img/avatar_default.png)
Documentation references Samsung S3C24xx and S3C64xx machine files in multiple places but the files were traveling around the kernel multiple times. Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org> Link: https://lore.kernel.org/r/20200911143343.498-1-krzk@kernel.org
172 lines
5.5 KiB
ReStructuredText
172 lines
5.5 KiB
ReStructuredText
====================
|
|
S3C24XX GPIO Control
|
|
====================
|
|
|
|
Introduction
|
|
------------
|
|
|
|
The s3c2410 kernel provides an interface to configure and
|
|
manipulate the state of the GPIO pins, and find out other
|
|
information about them.
|
|
|
|
There are a number of conditions attached to the configuration
|
|
of the s3c2410 GPIO system, please read the Samsung provided
|
|
data-sheet/users manual to find out the complete list.
|
|
|
|
See Documentation/arm/samsung/gpio.rst for the core implementation.
|
|
|
|
|
|
GPIOLIB
|
|
-------
|
|
|
|
With the event of the GPIOLIB in drivers/gpio, support for some
|
|
of the GPIO functions such as reading and writing a pin will
|
|
be removed in favour of this common access method.
|
|
|
|
Once all the extant drivers have been converted, the functions
|
|
listed below will be removed (they may be marked as __deprecated
|
|
in the near future).
|
|
|
|
The following functions now either have a `s3c_` specific variant
|
|
or are merged into gpiolib. See the definitions in
|
|
arch/arm/mach-s3c/gpio-cfg.h:
|
|
|
|
- s3c2410_gpio_setpin() gpio_set_value() or gpio_direction_output()
|
|
- s3c2410_gpio_getpin() gpio_get_value() or gpio_direction_input()
|
|
- s3c2410_gpio_getirq() gpio_to_irq()
|
|
- s3c2410_gpio_cfgpin() s3c_gpio_cfgpin()
|
|
- s3c2410_gpio_getcfg() s3c_gpio_getcfg()
|
|
- s3c2410_gpio_pullup() s3c_gpio_setpull()
|
|
|
|
|
|
GPIOLIB conversion
|
|
------------------
|
|
|
|
If you need to convert your board or driver to use gpiolib from the phased
|
|
out s3c2410 API, then here are some notes on the process.
|
|
|
|
1) If your board is exclusively using an GPIO, say to control peripheral
|
|
power, then it will require to claim the gpio with gpio_request() before
|
|
it can use it.
|
|
|
|
It is recommended to check the return value, with at least WARN_ON()
|
|
during initialisation.
|
|
|
|
2) The s3c2410_gpio_cfgpin() can be directly replaced with s3c_gpio_cfgpin()
|
|
as they have the same arguments, and can either take the pin specific
|
|
values, or the more generic special-function-number arguments.
|
|
|
|
3) s3c2410_gpio_pullup() changes have the problem that while the
|
|
s3c2410_gpio_pullup(x, 1) can be easily translated to the
|
|
s3c_gpio_setpull(x, S3C_GPIO_PULL_NONE), the s3c2410_gpio_pullup(x, 0)
|
|
are not so easy.
|
|
|
|
The s3c2410_gpio_pullup(x, 0) case enables the pull-up (or in the case
|
|
of some of the devices, a pull-down) and as such the new API distinguishes
|
|
between the UP and DOWN case. There is currently no 'just turn on' setting
|
|
which may be required if this becomes a problem.
|
|
|
|
4) s3c2410_gpio_setpin() can be replaced by gpio_set_value(), the old call
|
|
does not implicitly configure the relevant gpio to output. The gpio
|
|
direction should be changed before using gpio_set_value().
|
|
|
|
5) s3c2410_gpio_getpin() is replaceable by gpio_get_value() if the pin
|
|
has been set to input. It is currently unknown what the behaviour is
|
|
when using gpio_get_value() on an output pin (s3c2410_gpio_getpin
|
|
would return the value the pin is supposed to be outputting).
|
|
|
|
6) s3c2410_gpio_getirq() should be directly replaceable with the
|
|
gpio_to_irq() call.
|
|
|
|
The s3c2410_gpio and `gpio_` calls have always operated on the same gpio
|
|
numberspace, so there is no problem with converting the gpio numbering
|
|
between the calls.
|
|
|
|
|
|
Headers
|
|
-------
|
|
|
|
See arch/arm/mach-s3c/regs-gpio-s3c24xx.h for the list
|
|
of GPIO pins, and the configuration values for them. This
|
|
is included by using #include <mach/regs-gpio.h>
|
|
|
|
|
|
PIN Numbers
|
|
-----------
|
|
|
|
Each pin has an unique number associated with it in regs-gpio.h,
|
|
e.g. S3C2410_GPA(0) or S3C2410_GPF(1). These defines are used to tell
|
|
the GPIO functions which pin is to be used.
|
|
|
|
With the conversion to gpiolib, there is no longer a direct conversion
|
|
from gpio pin number to register base address as in earlier kernels. This
|
|
is due to the number space required for newer SoCs where the later
|
|
GPIOs are not contiguous.
|
|
|
|
|
|
Configuring a pin
|
|
-----------------
|
|
|
|
The following function allows the configuration of a given pin to
|
|
be changed.
|
|
|
|
void s3c_gpio_cfgpin(unsigned int pin, unsigned int function);
|
|
|
|
e.g.:
|
|
|
|
s3c_gpio_cfgpin(S3C2410_GPA(0), S3C_GPIO_SFN(1));
|
|
s3c_gpio_cfgpin(S3C2410_GPE(8), S3C_GPIO_SFN(2));
|
|
|
|
which would turn GPA(0) into the lowest Address line A0, and set
|
|
GPE(8) to be connected to the SDIO/MMC controller's SDDAT1 line.
|
|
|
|
|
|
Reading the current configuration
|
|
---------------------------------
|
|
|
|
The current configuration of a pin can be read by using standard
|
|
gpiolib function:
|
|
|
|
s3c_gpio_getcfg(unsigned int pin);
|
|
|
|
The return value will be from the same set of values which can be
|
|
passed to s3c_gpio_cfgpin().
|
|
|
|
|
|
Configuring a pull-up resistor
|
|
------------------------------
|
|
|
|
A large proportion of the GPIO pins on the S3C2410 can have weak
|
|
pull-up resistors enabled. This can be configured by the following
|
|
function:
|
|
|
|
void s3c_gpio_setpull(unsigned int pin, unsigned int to);
|
|
|
|
Where the to value is S3C_GPIO_PULL_NONE to set the pull-up off,
|
|
and S3C_GPIO_PULL_UP to enable the specified pull-up. Any other
|
|
values are currently undefined.
|
|
|
|
|
|
Getting and setting the state of a PIN
|
|
--------------------------------------
|
|
|
|
These calls are now implemented by the relevant gpiolib calls, convert
|
|
your board or driver to use gpiolib.
|
|
|
|
|
|
Getting the IRQ number associated with a PIN
|
|
--------------------------------------------
|
|
|
|
A standard gpiolib function can map the given pin number to an IRQ
|
|
number to pass to the IRQ system.
|
|
|
|
int gpio_to_irq(unsigned int pin);
|
|
|
|
Note, not all pins have an IRQ.
|
|
|
|
|
|
Author
|
|
-------
|
|
|
|
Ben Dooks, 03 October 2004
|
|
Copyright 2004 Ben Dooks, Simtec Electronics
|