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<a class="post-title-link" href="/2018/06/08/Linux-GPIO-Pinctrl-Subsystem/" itemprop="url">Linux GPIO-Pinctrl Subsystem</a></h2>
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<h3 id="前言"><a href="#前言" class="headerlink" title="前言"></a>前言</h3><p>对于一个IO Port来讲，有两方面需要配置，一是本身的功能设定，二是如果作为GPIO的话输入输出的设定。前者由Pin Controller控制，后者由GPIO Controller控制。</p>
<p>Pin Controller控制包括：</p>
<ul>
<li>引脚功能配置。例如该I/O pin是一个普通的GPIO还是一些特殊功能引脚（例如memeory bank上CS信号）。</li>
<li>引脚特性配置。例如pull-up/down电阻的设定，drive-strength的设定等。</li>
</ul>
<p>GPIO Controller控制包括：</p>
<ul>
<li>配置GPIO的方向</li>
<li>如果是输出，可以配置high level或者low level</li>
<li>如果是输入，可以获取GPIO引脚上的电平状态</li>
</ul>
<h3 id="软件架构"><a href="#软件架构" class="headerlink" title="软件架构"></a>软件架构</h3><p>linux kernel中的GPIO subsystem则用两个软件模块来对应上面两类硬件功能：</p>
<ul>
<li>pin control subsystem的模块图</li>
</ul>
<img src="/2018/06/08/Linux-GPIO-Pinctrl-Subsystem/pinctrl.png" title="Linux pinctrl">
<p>底层的pin controller driver是硬件相关的模组，初始化的时候会向pin control core模块注册pin control设备（通过pinctrl_register这个bootom level interface）。pin control core模块是一个硬件无关模块，它抽象了所有pin controller的硬件特性，仅仅从用户（各个driver就是pin control subsystem的用户）角度给出了top level的接口函数，这样，各个driver不需要关注pin controller的底层硬件相关的内容。</p>
<ul>
<li>GPIO subsystem的模块图</li>
</ul>
<img src="/2018/06/08/Linux-GPIO-Pinctrl-Subsystem/io.png" title="Linux gpio">
<p>基本上这个软件框架图和pin control subsystem是一样的，其软件抽象的思想也是一样的，当然其内部具体的实现不一样。</p>
<p>后对照Allwinner H5 Linux3.10的实际代码看，Pinctrl和Gpio是整合到一起的，传统gpio的调用最终还是到Pinctrl下面的API来实现。整体框架如下：<br><img src="/2018/06/08/Linux-GPIO-Pinctrl-Subsystem/sys.png" title="Linux pinctrl subsystem"></p>
<h5 id="1-普通Driver如何调用pinctrl"><a href="#1-普通Driver如何调用pinctrl" class="headerlink" title="1. 普通Driver如何调用pinctrl"></a>1. 普通Driver如何调用pinctrl</h5><p>上图从上往下看，普通Driver调用pin control subsystem的主要目标是：1.设定该设备的功能复用；2. 设定该device对应的那些pin的电气特性。以emmc模块驱动(<code>sunxi-mmc.c</code>)为例：<br>DTS中Emmc部分的配置为：<br><figure class="highlight dts"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="symbol">sdc0:</span> <span class="class">sdmmc@01c0f000 </span>{</span><br><span class="line"> compatible = <span class="string">"allwinner,sun50i-sdmmc0"</span>;</span><br><span class="line"> pinctrl-names = <span class="string">"default"</span>,<span class="string">"sleep"</span>;</span><br><span class="line"> pinctrl<span class="number">-0</span> = <span class="params"><<span class="variable">&sdc0_pins_a</span>></span>;</span><br><span class="line"> pinctrl<span class="number">-1</span> = <span class="params"><<span class="variable">&sdc0_pins_b</span>></span>;</span><br><span class="line">};</span><br></pre></td></tr></table></figure></p>
<p>Pinctrl部分的DTS配置为：<br><figure class="highlight mipsasm"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><span class="line"><span class="symbol">r_pio:</span> pinctrl@<span class="number">01</span>f02c00 {</span><br><span class="line"> compatible = <span class="string">"allwinner,sun50i-r-pinctrl"</span><span class="comment">;</span></span><br><span class="line"></span><br><span class="line"><span class="symbol"> sdc0_pins_a:</span> sdc0@<span class="number">0</span> {</span><br><span class="line"> allwinner,pins = <span class="string">"PF0"</span>, <span class="string">"PF1"</span>, <span class="string">"PF2"</span>, <span class="string">"PF3"</span>,<span class="string">"PF4"</span>,<span class="string">"PF5"</span><span class="comment">;</span></span><br><span class="line"> allwinner,function = <span class="string">"sdc0"</span><span class="comment">;</span></span><br><span class="line"> allwinner,muxsel = <<span class="number">2</span>><span class="comment">;</span></span><br><span class="line"> allwinner,drive = <<span class="number">1</span>><span class="comment">;</span></span><br><span class="line"> allwinner,pull = <<span class="number">1</span>><span class="comment">;</span></span><br><span class="line"> }<span class="comment">;</span></span><br><span class="line"></span><br><span class="line"><span class="symbol"> sdc0_pins_b:</span> sdc0@<span class="number">1</span> {</span><br><span class="line"> allwinner,pins = <span class="string">"PF0"</span>, <span class="string">"PF1"</span>, <span class="string">"PF2"</span>, <span class="string">"PF3"</span>,<span class="string">"PF4"</span>,<span class="string">"PF5"</span><span class="comment">;</span></span><br><span class="line"> allwinner,function = <span class="string">"io_disabled"</span><span class="comment">;</span></span><br><span class="line"> allwinner,muxsel = <<span class="number">7</span>><span class="comment">;</span></span><br><span class="line"> allwinner,drive = <<span class="number">1</span>><span class="comment">;</span></span><br><span class="line"> allwinner,pull = <<span class="number">1</span>><span class="comment">;</span></span><br><span class="line"> }<span class="comment">;</span></span><br></pre></td></tr></table></figure></p>
<p>其中pinctrl中有两种状态，default是默认状态，从上面dts配置可以看出配置为sdc0的Function，sleep是休眠时或是emmc关闭时调用的状态，从上可看出配置为io_disabled状态。<br>代码中调用的流程：<br><figure class="highlight pf"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">host->pinctrl = devm_pinctrl_get(&pdev->dev); </span><br><span class="line">--- <span class="number">1</span>. 获取设备（设备模型中的struct device）的pin control <span class="keyword">state</span> holder（struct pinctrl）</span><br><span class="line">host->pins_default = pinctrl_lookup_state(host->pinctrl,PINCTRL_STATE_DEFAULT); </span><br><span class="line">-- <span class="number">2</span>a. 根据<span class="keyword">state</span> name在pin control <span class="keyword">state</span> holder找到对应的pin control <span class="keyword">state</span>, 这里是<span class="keyword">default</span></span><br><span class="line">host->pins_sleep = pinctrl_lookup_state(host->pinctrl,PINCTRL_STATE_SLEEP);</span><br><span class="line">-- <span class="number">2</span>b. 这里是sleep状态</span><br><span class="line">ret = pinctrl_select_state(host->pinctrl , host->pins_sleep); -- <span class="number">3</span>a. 休眠时或是emmc关闭时调用</span><br><span class="line">rval = pinctrl_select_state(host->pinctrl, host->pins_default); -- <span class="number">3</span>b. 打开时调用</span><br></pre></td></tr></table></figure></p>
<h5 id="2-板级Pinctrl-driver如何注册"><a href="#2-板级Pinctrl-driver如何注册" class="headerlink" title="2. 板级Pinctrl driver如何注册"></a>2. 板级Pinctrl driver如何注册</h5><p>pinctrl driver根据pin controller的实际情况，实现struct pinctrl_desc（包括pin/pin group的抽象，function的抽象，pinconf、pinmux的operation API实现，dt_node_to_map的实现，等等），并注册到kernel中。<br>代码流程–><code>pinctrl-sun50iw1p1.c</code>开始：<br><figure class="highlight haskell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="title">sun50iw1p1_pinctrl_probe</span> </span><br><span class="line"> <span class="comment">--> sunxi_pinctrl_init(pdev,&sun50iw1p1_pinctrl_data); -- 其中sun50iw1p1_pinctrl_data描述了所有IO的Function及irq状况</span></span><br><span class="line"> <span class="comment">--></span></span><br><span class="line"> pctrl_desc->confops = &sunxi_pconf_ops; <span class="comment">-- 操作函数是用来配置引脚的特性,如pull-up/down，driver strength</span></span><br><span class="line"> pctrl_desc->pctlops = &sunxi_pctrl_ops; <span class="comment">-- dts 功能group的相关解析</span></span><br><span class="line"> pctrl_desc->pmxops = &sunxi_pmx_ops; <span class="comment">-- 功能复用enable/disable，gpio方向</span></span><br><span class="line"> <span class="comment">--></span></span><br><span class="line"> pctl->pctl_dev = pinctrl_register(pctrl_desc,&pdev->dev, pctl); <span class="comment">-- 注册到pin control subsystem</span></span><br></pre></td></tr></table></figure></p>
<h5 id="3-Gpio如何关联"><a href="#3-Gpio如何关联" class="headerlink" title="3. Gpio如何关联"></a>3. Gpio如何关联</h5><p>GPIO的HW block应该和其他功能复用的block是对等关系的，它们共同输入到一个复用器block，这个block的寄存器控制哪一个功能电路目前是active的。</p>
<img src="/2018/06/08/Linux-GPIO-Pinctrl-Subsystem/gpio.png" title="gpio">
<p>代码中，<code>sunxi_pinctrl_init(pdev,&sun50iw1p1_pinctrl_data)</code>–><br><figure class="highlight xl"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="title">pctl</span>-></span><span class="function"><span class="title">chip</span>-></span>request = sunxi_pinctrl_gpio_request,</span><br><span class="line"><span class="function"><span class="title">pctl</span>-></span><span class="function"><span class="title">chip</span>-></span>free = sunxi_pinctrl_gpio_free,</span><br><span class="line"><span class="function"><span class="title">pctl</span>-></span><span class="function"><span class="title">chip</span>-></span>direction_input = sunxi_pinctrl_gpio_direction_input,</span><br><span class="line"><span class="function"><span class="title">pctl</span>-></span><span class="function"><span class="title">chip</span>-></span>direction_output = sunxi_pinctrl_gpio_direction_output,</span><br><span class="line"><span class="function"><span class="title">pctl</span>-></span><span class="function"><span class="title">chip</span>-></span>get = sunxi_pinctrl_gpio_get,</span><br><span class="line"><span class="function"><span class="title">pctl</span>-></span><span class="function"><span class="title">chip</span>-></span>set = sunxi_pinctrl_gpio_set,</span><br><span class="line"><span class="function"><span class="title">pctl</span>-></span><span class="function"><span class="title">chip</span>-></span>set_debounce = sunxi_pinctrl_gpio_set_debounce,</span><br><span class="line"><span class="function"><span class="title">pctl</span>-></span><span class="function"><span class="title">chip</span>-></span>of_xlate = sunxi_pinctrl_gpio_of_xlate,</span><br><span class="line"><span class="function"><span class="title">pctl</span>-></span><span class="function"><span class="title">chip</span>-></span>to_irq = sunxi_pinctrl_gpio_to_irq,</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="title">ret</span> = gpiochip_add(pctl-></span>chip);</span><br><span class="line"><span class="keyword">if</span> (ret)</span><br><span class="line"> goto pinctrl_error;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="title">for</span> (i = 0; i < pctl-></span><span class="function"><span class="title">desc</span>-></span>npins; i++) {</span><br><span class="line"> <span class="function"><span class="title">const</span> struct sunxi_desc_pin *pin = pctl-></span><span class="function"><span class="title">desc</span>-></span>pins + i;</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">ret</span> = gpiochip_add_pin_range(pctl-></span><span class="function"><span class="title">chip</span>, dev_name(&pdev-></span>dev),</span><br><span class="line"> <span class="function"><span class="title">pin</span>-></span><span class="function"><span class="title">pin</span>.number - pctl-></span><span class="function"><span class="title">desc</span>-></span>pin_base,</span><br><span class="line"> <span class="function"><span class="title">pin</span>-></span>pin.number, <span class="number">1</span>);</span><br><span class="line"> <span class="keyword">if</span> (ret)</span><br><span class="line"> goto gpiochip_error;</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p>
<p>通过gpiochip_add(<code>gpiolib.c</code>)将 pctl->chip中指定的api与gpio子系统关联起来，以<code>gpiod_direction_output</code>为例：<br><figure class="highlight xl"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="title">gpiod_direction_output</span> ----></span> </span><br><span class="line"> <span class="function"><span class="title">chip</span>-></span><span class="function"><span class="title">direction_output</span>(chip, offset, value) ----></span></span><br><span class="line"> <span class="function"><span class="title">pctl</span>-></span><span class="function"><span class="title">chip</span>-></span><span class="function"><span class="title">direction_output</span> = sunxi_pinctrl_gpio_direction_output ----></span></span><br><span class="line"> <span class="function"><span class="title">pinctrl_gpio_direction_output</span>(chip-></span><span class="function"><span class="title">base</span> + offset) ----></span></span><br><span class="line"> <span class="function"><span class="title">pinctrl_gpio_direction</span>(gpio, <span class="literal">false</span>) ----></span></span><br><span class="line"> <span class="function"><span class="title">pinmux_gpio_direction</span>(pctldev, range, pin, input) ----></span></span><br><span class="line"> <span class="function"><span class="title">ops</span>-></span><span class="function"><span class="title">gpio_set_direction</span>(pctldev, range, pin, input) ----></span></span><br><span class="line"> <span class="function"><span class="title">sunxi_pmx_gpio_set_direction</span> ----></span> pinmux_ops里面的callback，所以最终回到pinctrl driver</span><br><span class="line"> <span class="function"><span class="title">sunxi_pmx_set</span>(pctldev, offset, desc-></span>muxval, <span class="literal">true</span>) -- 最终控制 寄存器的地方</span><br></pre></td></tr></table></figure></p>
<p>以上只是根据allwinner H5实际代码大略分析，具体可以参考以下。</p>
<h3 id="refs"><a href="#refs" class="headerlink" title="refs"></a>refs</h3><p><a href="http://www.wowotech.net/sort/gpio_subsystem" target="_blank" rel="noopener">Linux GOIO子系统-wowo</a></p>
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<h3 id="前言"><a href="#前言" class="headerlink" title="前言"></a>前言</h3><p>Linux Clock的框架图：</p>
<img src="/2018/06/07/Linux-clock-subsystem/ccf.png" title="CCF">
<p>以上的框架图就能说明整个clock子系统的运作情况，从上往下看，clock consumer – clock core – clock provider，同时通过DTS来配置串接。大多数Linux子系统中都呈现这种分层式架构。</p>
<p>clock consumer ：向其它driver提供操作clocks的通用API。<br>clock core：实现clock控制的通用逻辑，这部分和硬件无关。<br>clock provider：将和硬件相关的clock控制逻辑封装成操作函数集，交由底层的platform开发者实现，由通用逻辑调用。</p>
<h3 id="硬件相关"><a href="#硬件相关" class="headerlink" title="硬件相关"></a>硬件相关</h3><p>那么板子上clock相关模块到底是如何分布和规划的？</p>
<img src="/2018/06/07/Linux-clock-subsystem/clk-hw.png" title="Clock Hardware">
<p>上图从左往右看，最开始的源头产生：Oscillator –> 中间可能有倍频PLL、分频Divider、多路选择Mux、开关Gate –> clock使用的硬件模块。</p>
<p>也就是说，软件层面的架构 与 硬件层面的架构有一定程度的吻合。比如软件需要提供：1.Enable/Disable Clk；2. Set clk rate; 3. 选择clock的parent。 </p>
<h3 id="软件架构"><a href="#软件架构" class="headerlink" title="软件架构"></a>软件架构</h3><p>主要是如何体现clock consumer <---> clock core(CCF) <---> clock provider。两个层面问题，一是clock provider是如何注册进CCF的，二是clock consumer如何从CCF通过相应API获取对应的Clock控制。</---></---></p>
<h5 id="1-Clock-provider注册进CCF"><a href="#1-Clock-provider注册进CCF" class="headerlink" title="1.Clock provider注册进CCF"></a>1.Clock provider注册进CCF</h5><p>以Allwinner H5 Linux3.10为例，初始化的起点从start_kernel() 进入板级DT_MACHINE_START，如下：<br>linux-3.10\arch\arm\mach-sunxi\Sun50i.c<br><figure class="highlight stylus"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="title">DT_MACHINE_START</span><span class="params">(SUNXI_DT, CONFIG_SUNXI_SOC_NAME)</span></span></span><br><span class="line"> <span class="selector-class">.map_io</span> = sunxi_map_io,</span><br><span class="line"> <span class="selector-class">.init_time</span> = sunxi_timer_init,</span><br><span class="line"> <span class="selector-class">.dt_compat</span> = sunxi_board_dt_compat,</span><br><span class="line">MACHINE_END</span><br></pre></td></tr></table></figure></p>
<p>从sunxi_timer_init – > of_clk_init –> __clk_of_table中所有需要注册的各种类型clock – > linux-3.10\drivers\clk\sunxi\clk-sun50iw2.c 中CLK_OF_DECLARE定义的初始化函数。</p>
<p>以上有两个问题阐释下，一是<code>__clk_of_table</code>从何而来，二是具体初始化哪些clock类型。<br><code>__clk_of_table</code>是从所有<code>CLK_OF_DECLARE</code>定义而来，而初始化哪些clock则是由<code>CLK_OF_DECLARE</code>中的定义与Clock Provider DTS中的定义匹配而来，举个Fixed Clock的例子：<br>clk-sun50iw2.c中定义<code>CLK_OF_DECLARE(sunxi_fixed_clk, "allwinner,fixed-clock",of_sunxi_fixed_clk_setup);</code> ，而DTS(sun50iw1p1-clk.dtsi)中的定义：<br><figure class="highlight mipsasm"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* register fixed rate clock*/</span></span><br><span class="line"><span class="symbol"> clk_losc:</span> losc {</span><br><span class="line"> <span class="comment">#clock-cells = <0>;</span></span><br><span class="line"> compatible = <span class="string">"allwinner,fixed-clock"</span><span class="comment">;</span></span><br><span class="line"> <span class="keyword">clock-frequency </span>= <<span class="number">32768</span>><span class="comment">;</span></span><br><span class="line"> <span class="keyword">clock-output-names </span>= <span class="string">"losc"</span><span class="comment">;</span></span><br><span class="line"> }<span class="comment">;</span></span><br><span class="line"></span><br><span class="line"><span class="symbol"> clk_hosc:</span> hosc {</span><br><span class="line"> <span class="comment">#clock-cells = <0>;</span></span><br><span class="line"> compatible = <span class="string">"allwinner,fixed-clock"</span><span class="comment">;</span></span><br><span class="line"> <span class="keyword">clock-frequency </span>= <<span class="number">24000000</span>><span class="comment">;</span></span><br><span class="line"> <span class="keyword">clock-output-names </span>= <span class="string">"hosc"</span><span class="comment">;</span></span><br><span class="line"> }<span class="comment">;</span></span><br></pre></td></tr></table></figure></p>
<p>从上面可以看到是通过<code>allwinner,fixed-clock</code>字段来匹配的，匹配之后最终通过clk_register/of_clk_add_provider添加到CCF中以供Clock Consumer使用。这只是其中一种clock类型，那么还有哪些类型呢？<br>根据clock的特点，clock framework将clock分为fixed rate、gate、devider、mux、fixed factor、composite六类，每一类clock都有相似的功能、相似的控制方式，因而可以使用相同的逻辑，统一处理，这充分体现了面向对象的思想。</p>
<ul>
<li>fixed rate clock：具有固定的频率，不能开关、不能调整频率、不能选择parent、不需要提供任何的clk_ops回调函数，是最简单的一类clock。</li>
<li>gate clock：只可开关，会提供.enable/.disable回调。</li>
<li>divider clock：可以设置分频值，因而会提供.recalc_rate/.set_rate/.round_rate回调。</li>
<li>mux clock：可以选择多个parent，因为会实现.get_parent/.set_parent/.recalc_rate回调。</li>
<li>fixed factor clock：具有固定的factor（即multiplier和divider），clock的频率是由parent clock的频率，乘以mul，除以div，多用于一些具有固定分频系数的clock。由于parent clock的频率可以改变，因而fix factor clock也可该改变频率，因此也会提供.recalc_rate/.set_rate/.round_rate等回调。</li>
<li>composite clock：顾名思义，就是mux、divider、gate等clock的组合。</li>
</ul>
<h5 id="2-Clock-Consumer如何使用Clock"><a href="#2-Clock-Consumer如何使用Clock" class="headerlink" title="2.Clock Consumer如何使用Clock"></a>2.Clock Consumer如何使用Clock</h5><p>以Emmc模块为例，首先需要在DTS中EMMC相关部分配置，指明需要消费哪些Clock Provider中提供clock类型：<br><figure class="highlight dts"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="symbol">sdc2:</span> <span class="class">sdmmc@01C11000 </span>{</span><br><span class="line"> compatible = <span class="string">"allwinner,sun50i-sdmmc2"</span>;</span><br><span class="line"> ~~~~~~</span><br><span class="line"> clocks = <span class="params"><<span class="variable">&clk_hosc</span>></span>,<span class="params"><<span class="variable">&clk_pll_periph1x2</span>></span>,<span class="params"><<span class="variable">&clk_sdmmc2_mod</span>></span>,<span class="params"><<span class="variable">&clk_sdmmc2_bus</span>></span>,<span class="params"><<span class="variable">&clk_sdmmc2_rst</span>></span>;</span><br><span class="line"> clock-names = <span class="string">"osc24m"</span>,<span class="string">"pll_periph"</span>,<span class="string">"mmc"</span>,<span class="string">"ahb"</span>,<span class="string">"rst"</span>;</span><br><span class="line"> ~~~~~~</span><br><span class="line"> };</span><br></pre></td></tr></table></figure></p>
<p>如以上的clk_sdmmc2_mod、clk_sdmmc2_bus、clk_sdmmc2_rst就有在<code>sun50iw1p1-clk.dtsi</code>中定义。然后在emmc驱动相关代码中通过CCF提供的API取得相关clk并配置，如下(<code>sunxi-mmc.c</code>)：<br><figure class="highlight xl"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="title">host</span>-></span><span class="function"><span class="title">clk_mmc</span> = devm_clk_get(&pdev-></span>dev, <span class="string">"mmc"</span>); -- 取得clk</span><br><span class="line"><span class="function"><span class="title">if</span> (IS_ERR(host-></span>clk_mmc)) {</span><br><span class="line"> <span class="function"><span class="title">dev_err</span>(&pdev-></span>dev, <span class="string">"Could not get mmc clock\n"</span>);</span><br><span class="line"> <span class="function"><span class="title">ret</span> = PTR_ERR(host-></span>clk_mmc);</span><br><span class="line"> goto error_disable_regulator;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="title">ret</span> = clk_prepare_enable(host-></span>clk_mmc); -- 使能clk</span><br><span class="line"><span class="keyword">if</span> (ret) {</span><br><span class="line"> <span class="function"><span class="title">dev_err</span>(&pdev-></span>dev, <span class="string">"Enable mmc clk err %d\n"</span>, ret);</span><br><span class="line"> goto error_disable_clk_ahb;</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p>
<p>除了<code>devm_clk_get/clk_prepare_enable</code>外还有一些clock操作的API：</p>
<ul>
<li>clk_enable/clk_disable，启动/停止clock。不会睡眠。</li>
<li>clk_prepare/clk_unprepare，启动clock前的准备工作/停止clock后的善后工作。可能会睡眠。</li>
<li>clk_get_rate/clk_set_rate/clk_round_rate，clock频率的获取和设置，其中clk_set_rate可能会不成功（例如没有对应的分频比），此时会返回错误。如果要确保设置成功，则需要先调用clk_round_rate接口，得到和需要设置的rate比较接近的那个值。</li>
<li>获取/选择clock的parent clock。</li>
<li>clk_prepare_enable，将clk_prepare和clk_enable组合起来，一起调用。clk_disable_unprepare,将clk_disable和clk_unprepare组合起来，一起调用。</li>
</ul>
<p>更详细的解读可参考如下。</p>
<h3 id="ref"><a href="#ref" class="headerlink" title="ref"></a>ref</h3><p><a href="http://www.wowotech.net/linux_kenrel/clk_overview.html" target="_blank" rel="noopener">Linux common clock framework(1)_概述</a><br><a href="http://www.wowotech.net/pm_subsystem/ccf-arch.html" target="_blank" rel="noopener">Common Clock Framework系统结构</a></p>
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<h3 id="进程"><a href="#进程" class="headerlink" title="进程"></a>进程</h3><p>Linux内核中进程用task_struct结构体表示，称为进程描述符，该结构体相对比较复杂，有几百行代码，记载着该进程相关的所有信息，比如进程地址空间，进程状态，打开的文件等。对内核而言，进程或者线程都称为任务task。内核将所有进程放入一个双向循环链表结构的任务列表(task list)。</p>
<img src="/2018/05/17/Linux-process/task_struct.jpg" title="task_struct">
<p>Linux内核是抢占式多任务工作模式，进程大致分为两类（两者可相互转化）：</p>
<ul>
<li>守护进程（服务）: daemon,由内核在系统引导过程中启动的进程，和终端无关进程；</li>
<li>前台进程：跟终端相关，通过终端启动的进程（用户进程）；</li>
</ul>
<p>按进程占用资源的多少可以讲进程分为：</p>
<ul>
<li>CPU-Bound： CPU密集型（对CPU密集型是对cpu占用率高的进程），非交互；</li>
<li>IO-Bound： IO密集型（等待I/O时间长的进程），交互；</li>
</ul>
<h3 id="进程的状态"><a href="#进程的状态" class="headerlink" title="进程的状态"></a>进程的状态</h3><img src="/2018/05/17/Linux-process/ProcessState.png" title="Process State">
<ul>
<li><p>TASK_RUNNING<br>运行态： running<br>就绪态： ready（可以运行但是没运行）</p>
</li>
<li><p>TASK_INTERRUPTIBLE & TASK_UNINTERRUPTIBLE</p>
</li>
</ul>
<p>在linux系统中，一个进程无法获得某种资源，如锁（自旋锁、互斥锁、顺序锁、信号量等）、信号、中断，将进入等待状态，同时一个进程也可以根据需要主动进入等待状态。将进程从运行状态迁移到等待状态的方式：</p>
<ol>
<li>wait_event </li>
<li>wait_event_timeout </li>
<li>wait_event_interruptible </li>
<li>wait_event_interruptible_timeout </li>
</ol>
<p>1和2函数将进程放人等待队列中，并将当前进程的状态设置为TASK_UNINTERRUPTIBLE，即在等待队列中的进程不可以被信号激活，而只能由中断事件激活；<br>3和4函数将进程放人等待队列中，并将当前进程的状态设置为TASK_INTERRUPTIBLE，即在等待队列中的进程可以被信号和中断事件激活；<br>2和4函数会为当前等待进程设置一个定时器，当等待进程在指定的时间内没有被信号或者中断激活时，这个定时器将激活等待进程。 </p>
<ul>
<li><p>TASK_STOPPED<br>进程被停止执行，当进程接收到SIGSTOP、SIGTTIN、SIGTSTP或者SIGTTOU信号之后就会进入该状态。</p>
</li>
<li><p>EXIT_ZOMBIE<br>进程的执行被终止，但是其父进程还没有使用wait()等系统调用来获知它的终止信息，此时进程成为僵尸进程。</p>
</li>
<li><p>EXIT_DEAD<br>进程的最终状态。</p>
</li>
</ul>
<h3 id="创建新进程"><a href="#创建新进程" class="headerlink" title="创建新进程"></a>创建新进程</h3><p>分为三类：</p>
<ul>
<li>Linux进程创建</li>
<li>Linux用户级线程创建</li>
<li>Linux内核线程创建</li>
</ul>
<h4 id="Linux进程创建"><a href="#Linux进程创建" class="headerlink" title="Linux进程创建"></a>Linux进程创建</h4><p>通过fork()及exec()系统调用创建进程。</p>
<ul>
<li><p>fork: 采用复制当前进程的方式来创建子进程，此时子进程与父进程的区别仅在于pid, ppid以及资源统计量(比如挂起的信号)。</p>
</li>
<li><p>exec：读取可执行文件并载入地址空间执行；一般称之为exec函数族，有一系列exec开头的函数，比如execl, execve等。</p>
</li>
</ul>
<p>fork过程复制资源包括代码段，数据段，堆，栈。fork调用者所在进程便是父进程，新创建的进程便是子进程；在fork调用结束，从内核返回两次，一次继续执行父进程，一次进入执行子进程。</p>
<img src="/2018/05/17/Linux-process/fork_diagram.png" title="FORK">
<p>进程内存段：</p>
<img src="/2018/05/17/Linux-process/process_address_space.png" title="Process address space">
<p>exec执行的例子(<code>ls</code>)</p>
<img src="/2018/05/17/Linux-process/exec_ls.png" title="exec ls">
<h4 id="Linux用户级线程创建"><a href="#Linux用户级线程创建" class="headerlink" title="Linux用户级线程创建"></a>Linux用户级线程创建</h4><p>通过pthread库中的pthread_create()创建线程，也并非”轻量级进程”，在Linux看来线程是一种进程间共享资源的方式，线程可看做是跟其他进程共享资源的进程。</p>
<img src="/2018/05/17/Linux-process/do_fork.jpg">
<p>fork, vfork,clone根据不同参数调用do_fork：</p>
<ul>
<li>pthread_create: flags参数为 CLONE_VM, CLONE_FS, CLONE_FILES, CLONE_SIGHAND</li>
<li>fork: flags参数为 SIGCHLD</li>
<li>vfork: flags参数为 CLONE_VFORK, CLONE_VM, SIGCHLD</li>
</ul>
<p>所以进程与线程最大的区别在于资源是否共享，线程间共享的资源主要包括内存地址空间，文件系统，已打开文件，信号等信息， 如下图蓝色部分的flags便是线程创建过程所必需的参数。</p>
<img src="/2018/05/17/Linux-process/clone_flags.jpg">
<img src="/2018/05/17/Linux-process/process_and_thread.png">
<h4 id="Linux内核线程创建"><a href="#Linux内核线程创建" class="headerlink" title="Linux内核线程创建"></a>Linux内核线程创建</h4><p>通过kthread_create()创建内核线程，最初线程是停止的，需要使用wake_up_process启动它。它没有独立的地址空间，即mm指向NULL。这样的线程只在内核运行，不会切换到用户空间。所有内核线程都是由kthreadd作为内核线程的祖师爷，衍生而来的。</p>
<p>Linux内核可以看作一个服务进程(管理软硬件资源，响应用户进程的种种合理以及不合理的请求)。内核需要多个执行流并行，为了防止可能的阻塞，支持多线程是必要的。内核线程就是内核的分身，一个分身可以处理一件特定事情。内核线程的调度由内核负责，一个内核线程处于阻塞状态时不影响其他的内核线程，因为其是调度的基本单位。内核线程是直接由内核本身启动的进程。内核线程实际上是将内核函数委托给独立的进程，它与内核中的其他进程”并行”执行。内核线程经常被称之为内核守护进程。</p>
<p>内核线程主要有两种类型：</p>
<ol>
<li><p>线程启动后一直等待，直至内核请求线程执行某一特定操作。</p>
</li>
<li><p>线程启动后按周期性间隔运行，检测特定资源的使用，在用量超出或低于预置的限制时采取行动。</p>
</li>
</ol>
<h4 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h4><p>Linux使用task_struct来描述进程和线程：</p>
<p>一个进程由于其运行空间的不同, 从而有内核线程和用户进程的区分, 内核线程运行在内核空间, 之所以称之为线程是因为它没有虚拟地址空间, 只能访问内核的代码和数据, 而用户进程则运行在用户空间, 不能直接访问内核的数据但是可以通过中断, 系统调用等方式从用户态陷入内核态，但是内核态只是进程的一种状态, 与内核线程有本质区别。</p>
<p>用户进程运行在用户空间上, 而一些通过共享资源实现的一组进程我们称之为线程组, Linux下内核其实本质上没有线程的概念, Linux下线程其实上是与其他进程共享某些资源的进程而已。但是我们习惯上还是称他们为线程或者轻量级进程。</p>
<p>因此, Linux上进程分3种，内核线程（或者叫核心进程）、用户进程、用户线程, 当然如果更严谨的，你也可以认为用户进程和用户线程都是用户进程。</p>
<ul>
<li><p>内核线程拥有 进程描述符、PID、进程正文段、核心堆栈</p>
</li>
<li><p>用户进程拥有 进程描述符、PID、进程正文段、核心堆栈 、用户空间的数据段和堆栈</p>
</li>
<li><p>用户线程拥有 进程描述符、PID、进程正文段、核心堆栈，同父进程共享用户空间的数据段和堆栈</p>
</li>
</ul>
<h3 id="进程调度"><a href="#进程调度" class="headerlink" title="进程调度"></a>进程调度</h3><p>现在的操作系统都是多任务的，为了能让更多的任务能同时在系统上更好的运行，需要一个管理程序来管理计算机上同时运行的各个任务（也就是进程）。</p>
<p>这个管理程序就是调度程序，它的功能说起来很简单：</p>
<ol>
<li><p>决定哪些进程运行，哪些进程等待;</p>
</li>
<li><p>决定每个进程运行多长时间;</p>
</li>
</ol>
<p>此外，为了获得更好的用户体验，运行中的进程还可以立即被其他更紧急的进程打断。总之，调度是一个平衡的过程。一方面，它要保证各个运行的进程能够最大限度的使用CPU(即尽量少的切换进程，进程切换过多，CPU的时间会浪费在切换上)；另一方面，保证各个进程能公平的使用CPU(即防止一个进程长时间独占CPU的情况)。</p>
<img src="/2018/05/17/Linux-process/context_switching.png">