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gpio: OF: Cut painful BNF experiments from bindings

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In 2011 the commit bf859f84a1
("gpio/dt: Refine GPIO device tree binding") introduced an
experimental BNF notation for defining a regular grammar for
the GPIO phandles used by different devices.

This was an interesting approach, and shows that we have long
nutured the idea to formally verify device tree files using
regular grammar.

Most if not all other bindings use natural language to define
the bindings, and the recent thinking for verifying device
tree files is to use JSON schemas in separate definitions.

Cut the BNF business and replace it with natural language
so that it becomes more human-readable for now.

Cc: devicetree@vger.kernel.org
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Kumar Gala <galak@kernel.crashing.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
This commit is contained in:
Linus Walleij 2018-09-13 09:28:13 +02:00
parent 79b73ff9b2
commit 25db30c335
1 changed files with 60 additions and 46 deletions
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106
Documentation/devicetree/bindings/gpio/gpio.txt
View File

@ -1,18 +1,9 @@
Specifying GPIO information for devices
============================================
=======================================
1) gpios property
-----------------
Nodes that makes use of GPIOs should specify them using one or more
properties, each containing a 'gpio-list':
gpio-list ::= <single-gpio> [gpio-list]
single-gpio ::= <gpio-phandle> <gpio-specifier>
gpio-phandle : phandle to gpio controller node
gpio-specifier : Array of #gpio-cells specifying specific gpio
(controller specific)
GPIO properties should be named "[<name>-]gpios", with <name> being the purpose
of this GPIO for the device. While a non-existent <name> is considered valid
for compatibility reasons (resolving to the "gpios" property), it is not allowed
@ -236,46 +227,40 @@ Example of two SOC GPIO banks defined as gpio-controller nodes:
Some or all of the GPIOs provided by a GPIO controller may be routed to pins
on the package via a pin controller. This allows muxing those pins between
GPIO and other functions.
GPIO and other functions. It is a fairly common practice among silicon
engineers.
2.2) Ordinary (numerical) GPIO ranges
-------------------------------------
It is useful to represent which GPIOs correspond to which pins on which pin
controllers. The gpio-ranges property described below represents this, and
contains information structures as follows:
controllers. The gpio-ranges property described below represents this with
a discrete set of ranges mapping pins from the pin controller local number space
to pins in the GPIO controller local number space.
gpio-range-list ::= <single-gpio-range> [gpio-range-list]
single-gpio-range ::= <numeric-gpio-range> | <named-gpio-range>
numeric-gpio-range ::=
<pinctrl-phandle> <gpio-base> <pinctrl-base> <count>
named-gpio-range ::= <pinctrl-phandle> <gpio-base> '<0 0>'
pinctrl-phandle : phandle to pin controller node
gpio-base : Base GPIO ID in the GPIO controller
pinctrl-base : Base pinctrl pin ID in the pin controller
count : The number of GPIOs/pins in this range
The format is: <[pin controller phandle], [GPIO controller offset],
[pin controller offset], [number of pins]>;
The "pin controller node" mentioned above must conform to the bindings
described in ../pinctrl/pinctrl-bindings.txt.
The GPIO controller offset pertains to the GPIO controller node containing the
range definition.
In case named gpio ranges are used (ranges with both <pinctrl-base> and
<count> set to 0), the property gpio-ranges-group-names contains one string
for every single-gpio-range in gpio-ranges:
gpiorange-names-list ::= <gpiorange-name> [gpiorange-names-list]
gpiorange-name : Name of the pingroup associated to the GPIO range in
the respective pin controller.
The pin controller node referenced by the phandle must conform to the bindings
described in pinctrl/pinctrl-bindings.txt.
Elements of gpiorange-names-list corresponding to numeric ranges contain
the empty string. Elements of gpiorange-names-list corresponding to named
ranges contain the name of a pin group defined in the respective pin
controller. The number of pins/GPIOs in the range is the number of pins in
that pin group.
Each offset runs from 0 to N. It is perfectly fine to pile any number of
ranges with just one pin-to-GPIO line mapping if the ranges are concocted, but
in practice these ranges are often lumped in discrete sets.
Previous versions of this binding required all pin controller nodes that
were referenced by any gpio-ranges property to contain a property named
#gpio-range-cells with value <3>. This requirement is now deprecated.
However, that property may still exist in older device trees for
compatibility reasons, and would still be required even in new device
trees that need to be compatible with older software.
Example:
Example 1:
gpio-ranges = <&foo 0 20 10>, <&bar 10 50 20>;
This means:
- pins 20..29 on pin controller "foo" is mapped to GPIO line 0..9 and
- pins 50..69 on pin controller "bar" is mapped to GPIO line 10..29
Verbose example:
qe_pio_e: gpio-controller@1460 {
#gpio-cells = <2>;
@ -289,7 +274,28 @@ Here, a single GPIO controller has GPIOs 0..9 routed to pin controller
pinctrl1's pins 20..29, and GPIOs 10..29 routed to pin controller pinctrl2's
pins 50..69.
Example 2:
2.3) GPIO ranges from named pin groups
--------------------------------------
It is also possible to use pin groups for gpio ranges when pin groups are the
easiest and most convenient mapping.
Both both <pinctrl-base> and <count> must set to 0 when using named pin groups
names.
The property gpio-ranges-group-names must contain exactly one string for each
range.
Elements of gpio-ranges-group-names must contain the name of a pin group
defined in the respective pin controller. The number of pins/GPIO lines in the
range is the number of pins in that pin group. The number of pins of that
group is defined int the implementation and not in the device tree.
If numerical and named pin groups are mixed, the string corresponding to a
numerical pin range in gpio-ranges-group-names must be empty.
Example:
gpio_pio_i: gpio-controller@14b0 {
#gpio-cells = <2>;
@ -306,6 +312,14 @@ Example 2:
"bar";
};
Here, three GPIO ranges are defined wrt. two pin controllers. pinctrl1 GPIO
ranges are defined using pin numbers whereas the GPIO ranges wrt. pinctrl2
are named "foo" and "bar".
Here, three GPIO ranges are defined referring to two pin controllers.
pinctrl1 GPIO ranges are defined using pin numbers whereas the GPIO ranges
in pinctrl2 are defined using the pin groups named "foo" and "bar".
Previous versions of this binding required all pin controller nodes that
were referenced by any gpio-ranges property to contain a property named
#gpio-range-cells with value <3>. This requirement is now deprecated.
However, that property may still exist in older device trees for
compatibility reasons, and would still be required even in new device
trees that need to be compatible with older software.