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<div class=" wh_topic_content body "><main role="main"><article class="- topic/topic concept/concept topic concept" role="article" aria-labelledby="ariaid-title1">
<span class="edit-link" style="font-size:12px; opacity:0.6; text-align:right; vertical-align:middle"><a target="_blank" title="Edit this document" href="http://172.16.35.88/tasks/jdssno1uvvbf2mltu9kb9v3if05d5gopuakboe8hlud18rma/edit/F:/aicdita/aicdita-cn/topics/sdk/usb/usb-host-core.dita">Edit online</a></span><h1 class="- topic/title title topictitle1" id="ariaid-title1">USB Core</h1>
<div class="date inPage">15 Jan 2024</div><div style="color: gray;">
Read time: 6 minute(s)
</div>
<div class="- topic/body concept/conbody body conbody">
<section class="- topic/section section" id="usb_host_core__section_fvy_tnz_21c" data-ofbid="usb_host_core__section_fvy_tnz_21c"><h2 class="- topic/title title sectiontitle">Layer</h2>
<div class="- topic/p p" data-ofbid="d131208e38__20250123155212"><br/><div class="imagecenter"><img class="- topic/image image imagecenter" id="usb_host_core__image_gvy_tnz_21c" src="../../../images/usb/usb_host_drv_dev.png" alt="image1"/></div><br/></div>
<p class="- topic/p p" data-ofbid="d131208e45__20250123155212">由前几节可知 USB 将 <code class="+ topic/ph pr-d/codeph ph codeph">Device</code> 进一步细分成了 3 个层级： <code class="+ topic/ph pr-d/codeph ph codeph">Configuration</code> 配置、
<code class="+ topic/ph pr-d/codeph ph codeph">Interface</code> 接口、 <code class="+ topic/ph pr-d/codeph ph codeph">Endpoint</code> 端点。</p>
<p class="- topic/p p" data-ofbid="d131208e60__20250123155212">USB Core 为其中两个层次提供了 <code class="+ topic/ph pr-d/codeph ph codeph">Device + Driver</code> 的设备驱动模型，这两个层次分别是 <code class="+ topic/ph pr-d/codeph ph codeph">USB
Device Layer</code> 和 <code class="+ topic/ph pr-d/codeph ph codeph">USB Interface Layer</code> 层，一个 <code class="+ topic/ph pr-d/codeph ph codeph">USB
Device</code> 包含一个或多个 <code class="+ topic/ph pr-d/codeph ph codeph">USB Interface</code>。其中：</p>
<ul class="- topic/ul ul" id="usb_host_core__ul_hvy_tnz_21c" data-ofbid="usb_host_core__ul_hvy_tnz_21c">
<li class="- topic/li li" data-ofbid="d131208e80__20250123155212">
<p class="- topic/p p" data-ofbid="d131208e82__20250123155212"><code class="+ topic/ph pr-d/codeph ph codeph">USB Device Layer</code> 层。这一层的 <code class="+ topic/ph pr-d/codeph ph codeph">Device</code> 由
<code class="+ topic/ph pr-d/codeph ph codeph">Hub</code> 创建， <code class="+ topic/ph pr-d/codeph ph codeph">Hub</code> 本身也是一种 <code class="+ topic/ph pr-d/codeph ph codeph">USB
Device</code> 。这一层的 <code class="+ topic/ph pr-d/codeph ph codeph">Driver</code> 完成的功能非常简单，基本就是帮
<code class="+ topic/ph pr-d/codeph ph codeph">USB Device</code> 创建其包含的所有子 <code class="+ topic/ph pr-d/codeph ph codeph">USB Interface</code> 的
<code class="+ topic/ph pr-d/codeph ph codeph">Device</code> ，大部分场景下都是使用
<code class="+ topic/ph pr-d/codeph ph codeph">usb_generic_driver</code>。</p>
</li>
<li class="- topic/li li" data-ofbid="d131208e116__20250123155212">
<p class="- topic/p p" data-ofbid="d131208e118__20250123155212"><code class="+ topic/ph pr-d/codeph ph codeph">USB Interface Layer</code> 层。这一层的 <code class="+ topic/ph pr-d/codeph ph codeph">Device</code> 由上一级
<code class="+ topic/ph pr-d/codeph ph codeph">USB Device</code> 在驱动 probe() 时创建。而这一层的
<code class="+ topic/ph pr-d/codeph ph codeph">Driver</code> 就是普通的业务 Usb 驱动，即 Usb 协议中所说的 <code class="+ topic/ph pr-d/codeph ph codeph">Client
Software</code>。</p>
</li>
</ul>
</section>
<section class="- topic/section section" id="usb_host_core__section_ivy_tnz_21c" data-ofbid="usb_host_core__section_ivy_tnz_21c"><h2 class="- topic/title title sectiontitle">URB (USB Request Block)</h2>
<div class="- topic/p p" data-ofbid="d131208e143__20250123155212"><br/><div class="imagecenter"><img class="- topic/image image imagecenter" id="usb_host_core__image_jvy_tnz_21c" src="../../../images/usb/usb_host_urb.png" alt="image2"/></div><br/></div>
<p class="- topic/p p" data-ofbid="d131208e150__20250123155212">USB Core 除了提供上一节描述的设备驱动模型以外，另一个重要的作用就是要给 <code class="+ topic/ph pr-d/codeph ph codeph">USB Interface</code> Driver 提供读写
USB 数据的 API，这一任务是围绕着 <code class="+ topic/ph pr-d/codeph ph codeph">USB Request Block</code> 来完成的。</p>
<p class="- topic/p p" data-ofbid="d131208e159__20250123155212"><code class="+ topic/ph pr-d/codeph ph codeph">USB Interface</code> Driver 适配成功以后，会从配置信息中获取到当前 Interface 包含了多少个
<code class="+ topic/ph pr-d/codeph ph codeph">Endpoint</code> ，以及每个 <code class="+ topic/ph pr-d/codeph ph codeph">Endpoint</code> 的地址、传输类型、最大包长等其他信息。
<code class="+ topic/ph pr-d/codeph ph codeph">Endpoint</code> 是 USB 总线传输中最小的 <code class="+ topic/ph pr-d/codeph ph codeph">寻址单位</code> ，Interface Driver
利用对几个 <code class="+ topic/ph pr-d/codeph ph codeph">Endpoint</code> 的读写来驱动具体的设备功能。</p>
<p class="- topic/p p" data-ofbid="d131208e179__20250123155212">对某个 <code class="+ topic/ph pr-d/codeph ph codeph">Endpoint</code> 发起一次读写操作，具体工作使用 <code class="+ topic/ph pr-d/codeph ph codeph">struct urb</code>
数据结构来承担。</p>
<p class="- topic/p p" data-ofbid="d131208e189__20250123155212">以下是一个对 <code class="+ topic/ph pr-d/codeph ph codeph">Endpoint 0</code> 使用 urb 发起读写的一个简单实例：</p>
<pre class="+ topic/pre pr-d/codeblock pre codeblock language-c" id="usb_host_core__pre_kvy_tnz_21c" data-ofbid="usb_host_core__pre_kvy_tnz_21c"><code><strong class="hl-keyword">static</strong> <strong class="hl-keyword">int</strong> usb_internal_control_msg(<strong class="hl-keyword">struct</strong> usb_device *usb_dev,
<strong class="hl-keyword">unsigned</strong> <strong class="hl-keyword">int</strong> pipe,
<strong class="hl-keyword">struct</strong> usb_ctrlrequest *cmd,
<strong class="hl-keyword">void</strong> *data, <strong class="hl-keyword">int</strong> len, <strong class="hl-keyword">int</strong> timeout)
{
<strong class="hl-keyword">struct</strong> urb *urb;
<strong class="hl-keyword">int</strong> retv;
<strong class="hl-keyword">int</strong> length;
<em class="hl-comment">/* (1) 分配一个 urb 内存空间 */</em>
urb = usb_alloc_urb(<span class="hl-number">0</span>, GFP_NOIO);
<strong class="hl-keyword">if</strong> (!urb)
<strong class="hl-keyword">return</strong> -ENOMEM;
<em class="hl-comment">/* (2) 填充 urb 内容，最核心的有 3 方面：
1、总线地址：Device Num + Endpoint Num
2、数据：data + len
3、回调函数：usb_api_blocking_completion
*/</em>
usb_fill_control_urb(urb, usb_dev, pipe, (<strong class="hl-keyword">unsigned</strong> <strong class="hl-keyword">char</strong> *)cmd, data,
len, usb_api_blocking_completion, NULL);
<em class="hl-comment">/* (3) 发送 urb 请求，并且等待请求完成 */</em>
retv = usb_start_wait_urb(urb, timeout, &amp;length);
<strong class="hl-keyword">if</strong> (retv &lt; <span class="hl-number">0</span>)
<strong class="hl-keyword">return</strong> retv;
<strong class="hl-keyword">else</strong>
<strong class="hl-keyword">return</strong> length;
}
↓
<strong class="hl-keyword">static</strong> <strong class="hl-keyword">int</strong> usb_start_wait_urb(<strong class="hl-keyword">struct</strong> urb *urb, <strong class="hl-keyword">int</strong> timeout, <strong class="hl-keyword">int</strong> *actual_length)
{
<strong class="hl-keyword">struct</strong> api_context ctx;
<strong class="hl-keyword">unsigned</strong> <strong class="hl-keyword">long</strong> expire;
<strong class="hl-keyword">int</strong> retval;
init_completion(&amp;ctx.done);
urb-&gt;context = &amp;ctx;
urb-&gt;actual_length = <span class="hl-number">0</span>;
<em class="hl-comment">/* (3.1) 把 urb 请求挂载到 hcd 的队列当中 */</em>
retval = usb_submit_urb(urb, GFP_NOIO);
<strong class="hl-keyword">if</strong> (unlikely(retval))
<strong class="hl-keyword">goto</strong> out;
expire = timeout ? msecs_to_jiffies(timeout) : MAX_SCHEDULE_TIMEOUT;
<em class="hl-comment">/* (3.2) 当 urb 执行完成后，首先会调用 urb 的回调函数，然后会发送 completion 信号解除这里的阻塞 */</em>
<strong class="hl-keyword">if</strong> (!wait_for_completion_timeout(&amp;ctx.done, expire)) {
usb_kill_urb(urb);
retval = (ctx.status == -ENOENT ? -ETIMEDOUT : ctx.status);
dev_dbg(&amp;urb-&gt;dev-&gt;dev,
<span class="hl-string">"%s timed out on ep%d%s len=%u/%u\n"</span>,
current-&gt;comm,
usb_endpoint_num(&amp;urb-&gt;ep-&gt;desc),
usb_urb_dir_in(urb) ? <span class="hl-string">"in"</span> : <span class="hl-string">"out"</span>,
urb-&gt;actual_length,
urb-&gt;transfer_buffer_length);
} <strong class="hl-keyword">else</strong>
retval = ctx.status;
out:
<strong class="hl-keyword">if</strong> (actual_length)
*actual_length = urb-&gt;actual_length;
usb_free_urb(urb);
<strong class="hl-keyword">return</strong> retval;
}
</code></pre>
</section>
<section class="- topic/section section" id="usb_host_core__section_lvy_tnz_21c" data-ofbid="usb_host_core__section_lvy_tnz_21c"><h2 class="- topic/title title sectiontitle">Normal Device urb_enqueue</h2>
<p class="- topic/p p" data-ofbid="d131208e204__20250123155212">对普通的 Usb device 来说，urb 最后会提交到 Host Controller 的收发队列上面，由 HC 完成实际的 USB 传输：</p>
<pre class="+ topic/pre pr-d/codeblock pre codeblock language-c" id="usb_host_core__pre_mvy_tnz_21c" data-ofbid="usb_host_core__pre_mvy_tnz_21c"><code>usb_submit_urb() → usb_hcd_submit_urb():
<strong class="hl-keyword">int</strong> usb_hcd_submit_urb (<strong class="hl-keyword">struct</strong> urb *urb, gfp_t mem_flags)
{
<em class="hl-comment">/* (1) 如果是 roothub 走特殊的路径 */</em>
<strong class="hl-keyword">if</strong> (is_root_hub(urb-&gt;dev)) {
status = rh_urb_enqueue(hcd, urb);
<em class="hl-comment">/* (2) 如果是普通 device 调用对应的 hcd 的 urb_enqueue() 函数 */</em>
} <strong class="hl-keyword">else</strong> {
status = map_urb_for_dma(hcd, urb, mem_flags);
<strong class="hl-keyword">if</strong> (likely(status == <span class="hl-number">0</span>)) {
status = hcd-&gt;driver-&gt;urb_enqueue(hcd, urb, mem_flags);
<strong class="hl-keyword">if</strong> (unlikely(status))
unmap_urb_for_dma(hcd, urb);
}
}
}
</code></pre>
</section>
<section class="- topic/section section" id="usb_host_core__section_nvy_tnz_21c" data-ofbid="usb_host_core__section_nvy_tnz_21c"><h2 class="- topic/title title sectiontitle">7.12.5.1.2.2. Roothub Device urb_enqueue</h2>
<p class="- topic/p p" data-ofbid="d131208e216__20250123155212">特别需要注意的是 roothub 它是一个虚拟的 usb device，实际上它并不在 usb 总线上而是在 host 内部，所以相应的 urb 需要特殊处理，而不能使用
hcd 把数据发送到 Usb 总线上去。</p>
<pre class="+ topic/pre pr-d/codeblock pre codeblock language-c" id="usb_host_core__pre_ovy_tnz_21c" data-ofbid="usb_host_core__pre_ovy_tnz_21c"><code>usb_submit_urb() → usb_hcd_submit_urb() → rh_urb_enqueue():
<strong class="hl-keyword">static</strong> <strong class="hl-keyword">int</strong> rh_urb_enqueue (<strong class="hl-keyword">struct</strong> usb_hcd *hcd, <strong class="hl-keyword">struct</strong> urb *urb)
{
<em class="hl-comment">/* (1) 对于 int 类型的数据，被挂载到 hcd-&gt;status_urb 指针上面
通常 roothub 驱动用这个 urb 来查询 roothub 的端口状态
*/</em>
<strong class="hl-keyword">if</strong> (usb_endpoint_xfer_int(&amp;urb-&gt;ep-&gt;desc))
<strong class="hl-keyword">return</strong> rh_queue_status (hcd, urb);
<em class="hl-comment">/* (2) 对于 control 类型的数据，是想读取 roothub ep0 上的配置信息
使用软件来模拟这类操作的响应
*/</em>
<strong class="hl-keyword">if</strong> (usb_endpoint_xfer_control(&amp;urb-&gt;ep-&gt;desc))
<strong class="hl-keyword">return</strong> rh_call_control (hcd, urb);
<strong class="hl-keyword">return</strong> -EINVAL;
}
|→
<strong class="hl-keyword">static</strong> <strong class="hl-keyword">int</strong> rh_queue_status (<strong class="hl-keyword">struct</strong> usb_hcd *hcd, <strong class="hl-keyword">struct</strong> urb *urb)
{
<em class="hl-comment">/* (1.1) 将 urb 挂载到对应的 ep 链表中 */</em>
retval = usb_hcd_link_urb_to_ep(hcd, urb);
<strong class="hl-keyword">if</strong> (retval)
<strong class="hl-keyword">goto</strong> done;
<em class="hl-comment">/* (1.2) 将 urb 赋值给 hcd-&gt;status_urb
在 hcd 驱动中，会通过这些接口来通知 roothub 的端口状态变化
*/</em>
hcd-&gt;status_urb = urb;
urb-&gt;hcpriv = hcd; <em class="hl-comment">/* indicate it's queued */</em>
<strong class="hl-keyword">if</strong> (!hcd-&gt;uses_new_polling)
mod_timer(&amp;hcd-&gt;rh_timer, (jiffies/(HZ/<span class="hl-number">4</span>) + <span class="hl-number">1</span>) * (HZ/<span class="hl-number">4</span>));
}
|→
<strong class="hl-keyword">static</strong> <strong class="hl-keyword">int</strong> rh_call_control (<strong class="hl-keyword">struct</strong> usb_hcd *hcd, <strong class="hl-keyword">struct</strong> urb *urb)
{
<em class="hl-comment">/* (2.1) 软件模拟对 roothub 配置读写的响应 */</em>
}</code></pre>
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<div class=" wh_topic_toc "><div class="wh_topic_label">在本页上</div><ul><li class="section-item"><div class="section-title"><a href="#usb_host_core__section_fvy_tnz_21c" data-tocid="usb_host_core__section_fvy_tnz_21c">Layer</a></div></li><li class="section-item"><div class="section-title"><a href="#usb_host_core__section_ivy_tnz_21c" data-tocid="usb_host_core__section_ivy_tnz_21c">URB (USB Request Block)</a></div></li><li class="section-item"><div class="section-title"><a href="#usb_host_core__section_lvy_tnz_21c" data-tocid="usb_host_core__section_lvy_tnz_21c">Normal Device urb_enqueue</a></div></li><li class="section-item"><div class="section-title"><a href="#usb_host_core__section_nvy_tnz_21c" data-tocid="usb_host_core__section_nvy_tnz_21c">7.12.5.1.2.2. Roothub Device urb_enqueue</a></div></li></ul></div>
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