Linux reset子系统

骑猪看日落 2024-03-23 18:15 70阅读 0赞

## 1. 前言 ##

复杂IC内部有很多具有独立功能的硬件模块，例如CPU cores、GPU cores、USB控制器、MMC控制器、等等，出于功耗、稳定性等方面的考虑，有些IC在内部为这些硬件模块设计了复位信号（reset signals），软件可通过寄存器（一般1个bit控制1个硬件）控制这些硬件模块的复位状态。  
Linux kernel为了方便设备驱动的编写，抽象出一个简单的软件框架----reset framework，为reset的**provider**提供统一的reset资源管理手段，并为reset的**consumer**（各个硬件模块）提供便捷、统一的复位控制API。

## 2. 前言 ##

reset子系统也分为了consumer和provider，结构体关系如下：

## 3. consumer ##

对于一个具体的**硬件模块**，它的要求很简单：**复位我的硬件模块**，而不必关注具体复位的手段（例如控制哪个寄存器的哪个bit位，等等）。

Linux kernel基于device tree提供了对应的reset framework：

1.  首先，提供描述系统中reset资源的方法（参考provider的介绍），这样consumer可以基于这种描述，在自己的dts node中引用所需的reset信号。
2.  然后，consumer设备在自己的dts node中使用“resets”、“reset-names”等关键字声明所需的reset的资源，例如("resets"字段的具体格式由reset provider决定)：

<table> 
 <tbody> 
  <tr> 
   <td></td> 
   <td><code>device { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>resets = &lt;&amp;rst 20&gt;;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>reset-names = "reset"; </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>This represents a device with a single reset signal named "reset".</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>bus { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>resets = &lt;&amp;rst 10&gt; &lt;&amp;rst 11&gt; &lt;&amp;rst 12&gt; &lt;&amp;rst 11&gt;;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>reset-names = "i2s1", "i2s2", "dma", "mixer"; </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>This represents a bus that controls the reset signal of each of four sub- ordinate devices. Consider for example a bus that fails to operate unless no child device has reset asserted. </code></td> 
  </tr> 
 </tbody> 
</table>

1.  最后，consumer driver在需要的时候，可以调用下面的API复位自己（具体可参考"include\\linux\\reset.h"）：

*  只有一个reset信号的话，可以使用最简单的device\_reset API

<table> 
 <tbody> 
  <tr> 
   <td></td> 
   <td><code>static inline int __must_check device_reset(struct device *dev)</code></td> 
  </tr> 
 </tbody> 
</table>

*  如果需要更为复杂的控制（例如有多个reset信号、需要控制处于reset状态的长度的等），可以使用稍微复杂的API

<table> 
 <tbody> 
  <tr> 
   <td></td> 
   <td><code>/* 通过reset_control_get或者devm_reset_control_get获得reset句柄 */</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct reset_control *reset_control_get(struct device *dev, const char *id); </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct reset_control *devm_reset_control_get(struct device *dev, const char *id);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>/* 通过reset_control_put释放reset句柄 */</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>void reset_control_put(struct reset_control *rstc); </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>/* 通过reset_control_reset进行复位，或者通过reset_control_assert使设备处于复位生效状态，通过reset_control_deassert使复位失效 */</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>int reset_control_reset(struct reset_control *rstc); /先复位，延迟一会，然后解复位 </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>int reset_control_assert(struct reset_control *rstc); //复位 </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>int reset_control_deassert(struct reset_control *rstc);//解复位</code></td> 
  </tr> 
 </tbody> 
</table>

## 4. provider ##

kernel为reset provider提供的API位于"include/linux/reset-controller.h"中，很简单，无非就是：创建并填充reset controller设备（struct reset\_controller\_dev），并调用相应的接口:

*  reset\_controller\_register //注册reset\_controller
 *  reset\_controller\_unregister //注销reset\_controller

reset controller的抽象也很简单：

<table> 
 <tbody> 
  <tr> 
   <td></td> 
   <td><code>/**</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* struct reset_controller_dev - reset controller entity that might</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* provide multiple reset controls</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* @ops: a pointer to device specific struct reset_control_ops</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* @owner: kernel module of the reset controller driver</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* @list: internal list of reset controller devices</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* @reset_control_head: head of internal list of requested reset controls</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* @dev: corresponding driver model device struct</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* @of_node: corresponding device tree node as phandle target</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* @of_reset_n_cells: number of cells in reset line specifiers</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* @of_xlate: translation function to translate from specifier as found in the</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* device tree to id as given to the reset control ops, defaults</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* to :c:func:`of_reset_simple_xlate`.</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* @nr_resets: number of reset controls in this reset controller device</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>*/</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct reset_controller_dev { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>const struct reset_control_ops *ops;//ops提供reset操作的实现，基本上是reset provider的所有工作量。</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct module *owner;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct list_head list;全局链表，复位控制器注册后挂载到全局链表</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct list_head reset_control_head;各个模块复位的链表头</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct device *dev;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct device_node *of_node;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>int of_reset_n_cells;用于解析consumer device dts node中的“resets = &lt;&gt;; ”节点,指示dts中引用时，需要几个参数</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>int (*of_xlate)(struct reset_controller_dev *rcdev,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>const struct of_phandle_args *reset_spec);//用于解析consumer device dts node中的“resets = &lt;&gt;; ”节点</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>unsigned int nr_resets;//该reset controller所控制的reset信号的个数</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
 </tbody> 
</table>

struct reset\_control\_ops也比较单纯，如下：

<table> 
 <tbody> 
  <tr> 
   <td></td> 
   <td><code>/**</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* struct reset_control_ops - reset controller driver callbacks</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>*</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* @reset: for self-deasserting resets, does all necessary</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* things to reset the device</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* @assert: manually assert the reset line, if supported</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* @deassert: manually deassert the reset line, if supported</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* @status: return the status of the reset line, if supported</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>*/</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct reset_control_ops { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>int (*reset)(struct reset_controller_dev *rcdev, unsigned long id); //控制设备完成一次完整的复位过程</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>int (*assert)(struct reset_controller_dev *rcdev, unsigned long id); //控制设备reset状态的生效</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>int (*deassert)(struct reset_controller_dev *rcdev, unsigned long id);//控制设备reset状态的失效。</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>int (*status)(struct reset_controller_dev *rcdev, unsigned long id); //复位状态查询</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
 </tbody> 
</table>

## 5. reset驱动的设备树描述总结 ##

### 5.1 对于provider ###

<table> 
 <tbody> 
  <tr> 
   <td></td> 
   <td><code>reset:reset-controller{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>compatible = "xx,xx-reset";</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>reg = &lt;0x0 0x30390000 0x0 0x10000&gt;;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>#reset-cells = &lt;1&gt;;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
 </tbody> 
</table>

上述是一个reset控制器的节点，0x30390000 是寄存器基址，0x1000是映射大小。"\#reset-cells"代表引用该reset时需要的cells个数。

### 5.2 对于consumer ###

例如，\#reset-cells = <1>; 则正确引用为：

<table> 
 <tbody> 
  <tr> 
   <td></td> 
   <td><code>mmc:mmc@0x12345678{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>......</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>resets = &lt;&amp;reset 0&gt;;//0代表reset设备id，id是自定义的，但是不能超过reset驱动中指定的设备个数</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>......</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
 </tbody> 
</table>

## 6. 开源reset驱动实例 ##

### 6.1 实例1(比较容易理解) ###

> 设备树： arch/arm/boot/dts/imx7d.dtsi

<table> 
 <tbody> 
  <tr> 
   <td></td> 
   <td><code>pcie: pcie@0x33800000 { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>compatible = "fsl,imx7d-pcie", "snps,dw-pcie";</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>....</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>resets = &lt;&amp;src IMX7_RESET_PCIEPHY&gt;,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>&lt;&amp;src IMX7_RESET_PCIE_CTRL_APPS_EN&gt;;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>reset-names = "pciephy", "apps";</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>status = "disabled";</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
 </tbody> 
</table>

> 驱动代码： drivers/reset/reset-imx7.c

<table> 
 <tbody> 
  <tr> 
   <td></td> 
   <td><code>...</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct imx7_src { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct reset_controller_dev rcdev;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct regmap *regmap;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>enum imx7_src_registers { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>SRC_A7RCR0 = 0x0004,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>SRC_M4RCR = 0x000c,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>SRC_ERCR = 0x0014,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>SRC_HSICPHY_RCR = 0x001c,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>SRC_USBOPHY1_RCR = 0x0020,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>SRC_USBOPHY2_RCR = 0x0024,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>SRC_MIPIPHY_RCR = 0x0028,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>SRC_PCIEPHY_RCR = 0x002c,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>SRC_DDRC_RCR = 0x1000,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct imx7_src_signal { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>unsigned int offset, bit;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static const struct imx7_src_signal imx7_src_signals[IMX7_RESET_NUM] = { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>[IMX7_RESET_A7_CORE_POR_RESET0] = { SRC_A7RCR0, BIT(0) },</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>[IMX7_RESET_A7_CORE_POR_RESET1] = { SRC_A7RCR0, BIT(1) },</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>[IMX7_RESET_A7_CORE_RESET0] = { SRC_A7RCR0, BIT(4) },</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>[IMX7_RESET_A7_CORE_RESET1] = { SRC_A7RCR0, BIT(5) },</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>[IMX7_RESET_A7_DBG_RESET0] = { SRC_A7RCR0, BIT(8) },</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>[IMX7_RESET_A7_DBG_RESET1] = { SRC_A7RCR0, BIT(9) },</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>...</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static struct imx7_src *to_imx7_src(struct reset_controller_dev *rcdev)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return container_of(rcdev, struct imx7_src, rcdev);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static int imx7_reset_set(struct reset_controller_dev *rcdev,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>unsigned long id, bool assert)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct imx7_src *imx7src = to_imx7_src(rcdev);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>const struct imx7_src_signal *signal = &amp;imx7_src_signals[id];</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>unsigned int value = assert ? signal-&gt;bit : 0;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>switch (id) { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>case IMX7_RESET_PCIEPHY:</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>/*</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* wait for more than 10us to release phy g_rst and</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>* btnrst</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>*/</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>if (!assert)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>udelay(10);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>break;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>case IMX7_RESET_PCIE_CTRL_APPS_EN:</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>value = (assert) ? 0 : signal-&gt;bit;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>break;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return regmap_update_bits(imx7src-&gt;regmap,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>signal-&gt;offset, signal-&gt;bit, value);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static int imx7_reset_assert(struct reset_controller_dev *rcdev,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>unsigned long id)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return imx7_reset_set(rcdev, id, true);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static int imx7_reset_deassert(struct reset_controller_dev *rcdev,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>unsigned long id)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return imx7_reset_set(rcdev, id, false);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static const struct reset_control_ops imx7_reset_ops = { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>.assert = imx7_reset_assert,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>.deassert = imx7_reset_deassert,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static int imx7_reset_probe(struct platform_device *pdev)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct imx7_src *imx7src;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct device *dev = &amp;pdev-&gt;dev;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct regmap_config config = { .name = "src" };</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>imx7src = devm_kzalloc(dev, sizeof(*imx7src), GFP_KERNEL);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>if (!imx7src)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return -ENOMEM;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>imx7src-&gt;regmap = syscon_node_to_regmap(dev-&gt;of_node);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>if (IS_ERR(imx7src-&gt;regmap)) { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>dev_err(dev, "Unable to get imx7-src regmap");</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return PTR_ERR(imx7src-&gt;regmap);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>regmap_attach_dev(dev, imx7src-&gt;regmap, &amp;config);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>imx7src-&gt;rcdev.owner = THIS_MODULE;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>imx7src-&gt;rcdev.nr_resets = IMX7_RESET_NUM;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>imx7src-&gt;rcdev.ops = &amp;imx7_reset_ops;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>imx7src-&gt;rcdev.of_node = dev-&gt;of_node;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return devm_reset_controller_register(dev, &amp;imx7src-&gt;rcdev);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static const struct of_device_id imx7_reset_dt_ids[] = { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ .compatible = "fsl,imx7d-src", },</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ /* sentinel */ },</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static struct platform_driver imx7_reset_driver = { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>.probe = imx7_reset_probe,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>.driver = { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>.name = KBUILD_MODNAME,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>.of_match_table = imx7_reset_dt_ids,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>},</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>builtin_platform_driver(imx7_reset_driver);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
 </tbody> 
</table>

--------------------

### 6.2 实例2(在gpio子系统中嵌套reset子系统) ###

> 设备树： arc/arm64/boot/dts/myzr/myimx8mm.dts

<table> 
 <tbody> 
  <tr> 
   <td></td> 
   <td><code>&amp;pcie0{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>pinctrl-names = "default";</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>pinctrl-0 = &lt;&amp;pinctrl_i2c4_pcieclk&gt;, &lt;&amp;pinctrl_gpio1_pciendis&gt;, &lt;&amp;pinctrl_sd2_pciewake&gt;, &lt;&amp;pinctrl_sai2_pcienrst&gt;;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>disable-gpio = &lt;&amp;gpio1 5 GPIO_ACTIVE_LOW&gt;;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>reset-gpio = &lt;&amp;gpio4 21 GPIO_ACTIVE_LOW&gt;;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>ext_osc = &lt;1&gt;;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>status = "okay";</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
 </tbody> 
</table>

> 驱动代码： drivers/reset/gpio-reset.c

<table> 
 <tbody> 
  <tr> 
   <td></td> 
   <td><code>...</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct gpio_reset_data { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct reset_controller_dev rcdev;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>unsigned int gpio;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>bool active_low;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>s32 delay_us;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>s32 post_delay_ms;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static void gpio_reset_set(struct reset_controller_dev *rcdev, int asserted)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct gpio_reset_data *drvdata = container_of(rcdev,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct gpio_reset_data, rcdev);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>int value = asserted;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>if (drvdata-&gt;active_low)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>value = !value;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>gpio_set_value_cansleep(drvdata-&gt;gpio, value);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static int gpio_reset(struct reset_controller_dev *rcdev, unsigned long id)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct gpio_reset_data *drvdata = container_of(rcdev,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct gpio_reset_data, rcdev);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>if (drvdata-&gt;delay_us &lt; 0)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return -ENOSYS;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>gpio_reset_set(rcdev, 1);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>udelay(drvdata-&gt;delay_us);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>gpio_reset_set(rcdev, 0);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>if (drvdata-&gt;post_delay_ms &lt; 0)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return 0;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>msleep(drvdata-&gt;post_delay_ms);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return 0;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static int gpio_reset_assert(struct reset_controller_dev *rcdev,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>unsigned long id)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>gpio_reset_set(rcdev, 1);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return 0;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static int gpio_reset_deassert(struct reset_controller_dev *rcdev,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>unsigned long id)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>gpio_reset_set(rcdev, 0);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return 0;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static struct reset_control_ops gpio_reset_ops = { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>.reset = gpio_reset,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>.assert = gpio_reset_assert,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>.deassert = gpio_reset_deassert,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static int of_gpio_reset_xlate(struct reset_controller_dev *rcdev,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>const struct of_phandle_args *reset_spec)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>if (WARN_ON(reset_spec-&gt;args_count != 0))</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return -EINVAL;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return 0;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static int gpio_reset_probe(struct platform_device *pdev)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>...</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>drvdata = devm_kzalloc(&amp;pdev-&gt;dev, sizeof(*drvdata), GFP_KERNEL);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>...</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>drvdata-&gt;rcdev.of_node = np;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>drvdata-&gt;rcdev.owner = THIS_MODULE;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>drvdata-&gt;rcdev.nr_resets = 1; 该reset controller所控制的reset信号的个数</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>drvdata-&gt;rcdev.ops = &amp;gpio_reset_ops; //ops提供reset操作的实现。</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>drvdata-&gt;rcdev.of_xlate = of_gpio_reset_xlate; </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>reset_controller_register(&amp;drvdata-&gt;rcdev); //注册reset controller</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return 0;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static int gpio_reset_remove(struct platform_device *pdev)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>struct gpio_reset_data *drvdata = platform_get_drvdata(pdev);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>reset_controller_unregister(&amp;drvdata-&gt;rcdev);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return 0;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static struct of_device_id gpio_reset_dt_ids[] = { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ .compatible = "gpio-reset" },</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ }</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>#ifdef CONFIG_PM_SLEEP</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static int gpio_reset_suspend(struct device *dev)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>pinctrl_pm_select_sleep_state(dev);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return 0;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static int gpio_reset_resume(struct device *dev)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>pinctrl_pm_select_default_state(dev);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return 0;</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>#endif</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static const struct dev_pm_ops gpio_reset_pm_ops = { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>SET_LATE_SYSTEM_SLEEP_PM_OPS(gpio_reset_suspend, gpio_reset_resume)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static struct platform_driver gpio_reset_driver = { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>.probe = gpio_reset_probe,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>.remove = gpio_reset_remove,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>.driver = { </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>.name = "gpio-reset",</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>.owner = THIS_MODULE,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>.of_match_table = of_match_ptr(gpio_reset_dt_ids),</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>.pm = &amp;gpio_reset_pm_ops,</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>},</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>};</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static int __init gpio_reset_init(void)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>return platform_driver_register(&amp;gpio_reset_driver);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>arch_initcall(gpio_reset_init);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>static void __exit gpio_reset_exit(void)</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>{ </code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>platform_driver_unregister(&amp;gpio_reset_driver);</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>}</code></td> 
  </tr> 
  <tr> 
   <td></td> 
   <td><code>...</code></td> 
  </tr> 
 </tbody> 
</table>

## 7. reset驱动的实质 ##