查看“Reset overview”的源代码

The Linux<sup>&reg;</sup> kernel reset framework offers a generic API for reset lines management at platform level.<br />
<br>

== Framework purpose ==
The purpose of this article is to introduce the Linux kernel Reset Framework.
It provides general information and, based on concrete IP use cases, explains how to use it. 

<br/>
The Linux Reset framework offers a generic API for abstracting and controlling the different reset lines of the platform.<br/>
Reset lines can be internal system reset signals or external lines such as a GPIO to reset an external device.

==System overview==
{{
ImageMap|Image:Reset overview.png {{!}} frame {{!}} center{{!}} Reset Overview
rect 322 527 422 555 [[RCC internal peripheral | RCC]]
}}

===Component description===
*'''reset core:''' kernel reset framework designed for abstracting device reset handling via GPIOs or internal reset controller modules.<br/>
*'''reset-stm32mp1:''' STM32MP1 RCC specific reset driver
*'''RCC:''' Reset and clock controller that generates the different internal reset lines on STM32MP1.
<br/>

===API description===
Documentation on the reset interface can be found in kernel documentation folder: https://www.kernel.org/doc/Documentation/devicetree/bindings/reset/reset.txt
*Kernel reset API

To get the line reset from DT:
:*'''devm_reset_control_get_exclusive:''' looks up and obtains an exclusive reference to a reset controller (cannot be shared with another driver).
:*'''devm_reset_control_get_shared:''' looks up and obtains a shared reference to reset a controller (can be shared with another driver).

:*'''devm_reset_control_get:''' same as devm_reset_control_get_exclusive.

:*'''devm_reset_control_get_optional:''' same as devm_reset_control_get except that the reference name is optional.

:*'''devm_reset_control_get_optional_exclusive:''' same as devm_reset_control_get_exclusive except that the reference name is optional.
:*'''devm_reset_control_get_optional_shared:''' same as devm_reset_control_get_shared except that the reference name is optional.

To configure the reset line and retrieve its status from DT:
:*'''reset_control_assert:''' asserts the reset line
:*'''reset_control_deassert:''' deasserts the reset line 
:*'''reset_control_status:''' returns if the line is asserted or not

==Configuration==
===Kernel configuration===

By default, the activation of the Reset framework configuration (CONFIG_RESET_CONTROLER) is selected in the kernel configuration, through the Linux Menuconfig tool: [[Menuconfig or how to configure kernel]] (CONFIG_ARCH_STM32=y, CONFIG_ARCH_MULTI_V7=y):

===Device tree configuration===
A detailed device tree configuration is described in [[Reset device tree configuration]].

== How to use the Reset framework==
To control a peripheral reset line, a driver must first get a reference on the reset handler thanks to its device tree node.<br/>
The driver can then assert and deassert the reset line by calling the reset framework API.<br/>

Below an example:

 	foo: foo@adcdefgh {
                compatible = "foo-driver";
                ...
 		'''resets = <&rcc FOO_R>;'''
                ...
 	};

Before using the reset specified in the device tree node, the foo driver has to request it at probe execution.
 	static int foo_probe(struct platform_device *pdev)
 	{
 		'''struct reset_control *rst;'''
 		...
 		rst = '''devm_reset_control_get_exclusive(&pdev->dev, NULL)''';
 		if (IS_ERR(rst)) {
 			ret = PTR_ERR(rest);
 			dev_err(&pdev->dev, "reset get failed: %d\n", ret);
 			goto err_master_put;
 		}
 		...

The reset can then be asserted or deasserted using the reset framework API:

                ...
                '''reset_control_assert(rst);'''
                udelay(2);
                '''reset_control_deassert(rst);'''
                ...

==Source code location==
Reset core file <ref>{{CodeSource | Linux kernel | drivers/reset/core.c}}</ref>
<br>
STM32MP1 reset file <ref>{{CodeSource | Linux kernel | drivers/reset/reset-stm32mp1.c}}</ref>
<br>
STM32MP1 reset interface file <ref>{{CodeSource | Linux kernel | include/dt-bindings/reset/stm32mp1-resets.h}}</ref>

==References==
<references />

<noinclude>
{{ArticleBasedOnModel | Framework overview article model}}
{{PublicationRequestId | 10343 | 2019-01-21 | AnneJ}}
[[Category:Reset]]
</noinclude>