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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" href="http://172.16.35.88/tasks/jdssno1uvvbf2mltu9kb9v3if05d5gopuakboe8hlud18rma/edit/F:/aicdita/aicdita-cn/topics/sdk/usb/usb-gadget_bus.dita">Edit online</a></span><h1 class="- topic/title title topictitle1" id="ariaid-title1">Gadget Bus</h1><div class="date inPage">3 Apr 2024</div><div style="color: gray;">
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Read time: 4 minute(s)
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</div><div class="- topic/body concept/conbody body conbody"><p class="- topic/p p" data-ofbid="d354177e22__20250121172132">Gadget Layer 层没有定义一个标准的 Bus 总线，而是自定义了两条链表来分别存储 Device 和 Driver：</p><div class="table-container"><table class="- topic/table table frame-all" id="usb_gadget_bus__table_f3c_5qz_21c" data-ofbid="usb_gadget_bus__table_f3c_5qz_21c" data-cols="3"><caption></caption><colgroup><col style="width:21.691973969631235%"/><col style="width:38.6117136659436%"/><col style="width:39.69631236442516%"/></colgroup><thead class="- topic/thead thead"><tr class="- topic/row"><th class="- topic/entry entry colsep-1 rowsep-1" id="usb_gadget_bus__table_f3c_5qz_21c__entry__1">type</th><th class="- topic/entry entry colsep-1 rowsep-1" id="usb_gadget_bus__table_f3c_5qz_21c__entry__2">list</th><th class="- topic/entry entry colsep-0 rowsep-1" id="usb_gadget_bus__table_f3c_5qz_21c__entry__3">escript</th></tr></thead><tbody class="- topic/tbody tbody"><tr class="- topic/row"><td class="- topic/entry entry colsep-1 rowsep-1" headers="usb_gadget_bus__table_f3c_5qz_21c__entry__1">Device</td><td class="- topic/entry entry colsep-1 rowsep-1" headers="usb_gadget_bus__table_f3c_5qz_21c__entry__2">udc_list</td><td class="- topic/entry entry colsep-0 rowsep-1" headers="usb_gadget_bus__table_f3c_5qz_21c__entry__3">所有 Device 全集</td></tr><tr class="- topic/row"><td class="- topic/entry entry colsep-1 rowsep-0" headers="usb_gadget_bus__table_f3c_5qz_21c__entry__1">Driver</td><td class="- topic/entry entry colsep-1 rowsep-0" headers="usb_gadget_bus__table_f3c_5qz_21c__entry__2">gadget_driver_pending_list</td><td class="- topic/entry entry colsep-0 rowsep-0" headers="usb_gadget_bus__table_f3c_5qz_21c__entry__3">只包含没有适配 Device 的 Driver</td></tr></tbody></table></div><p class="- topic/p p" data-ofbid="d354177e52__20250121172132">它们的使用场景如下：</p><ul class="- topic/ul ul" id="usb_gadget_bus__ul_g3c_5qz_21c" data-ofbid="usb_gadget_bus__ul_g3c_5qz_21c"><li class="- topic/li li" data-ofbid="d354177e55__20250121172132">
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<div class="- topic/p p" data-ofbid="d354177e57__20250121172132">在 Gadget Device 创建时，首先把 Device 加入到 <code class="+ topic/ph pr-d/codeph ph codeph">udc_list</code> 链表，然后尝试和
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<code class="+ topic/ph pr-d/codeph ph codeph">gadget_driver_pending_list</code> 链表中的 Driver 进行
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match():<pre class="+ topic/pre pr-d/codeblock pre codeblock language-c" id="usb_gadget_bus__pre_h3c_5qz_21c" data-ofbid="usb_gadget_bus__pre_h3c_5qz_21c">usb_add_gadget_udc() → usb_add_gadget_udc_release() → usb_add_gadget():
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<strong class="hl-keyword">int</strong> usb_add_gadget(<strong class="hl-keyword">struct</strong> usb_gadget *gadget)
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{
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<em class="hl-comment">/* (1) 将 device 加入全局链表 */</em>
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list_add_tail(&udc->list, &udc_list);
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<em class="hl-comment">/* pick up one of pending gadget drivers */</em>
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<em class="hl-comment">/* (2) 尝试 match gadget 的 device 和 driver */</em>
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ret = check_pending_gadget_drivers(udc);
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<strong class="hl-keyword">if</strong> (ret)
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<strong class="hl-keyword">goto</strong> err_del_udc;
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mutex_unlock(&udc_lock);
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}
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↓
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<strong class="hl-keyword">static</strong> <strong class="hl-keyword">int</strong> check_pending_gadget_drivers(<strong class="hl-keyword">struct</strong> usb_udc *udc)
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{
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<strong class="hl-keyword">struct</strong> usb_gadget_driver *driver;
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<strong class="hl-keyword">int</strong> ret = <span class="hl-number">0</span>;
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<em class="hl-comment">/* (2.1) 遍历 `gadget_driver_pending_list` 链表中的 Driver，和 Device 进行 match()
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且一个 Driver 只能 match 一个 Device，Driver match 成功后会从链表删除
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*/</em>
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list_for_each_entry(driver, &gadget_driver_pending_list, pending)
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<strong class="hl-keyword">if</strong> (!driver->udc_name || strcmp(driver->udc_name,
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dev_name(&udc->dev)) == <span class="hl-number">0</span>) {
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<em class="hl-comment">/* (2.2) Match 成功，对 Device 和 Driver 进行 bind() */</em>
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ret = udc_bind_to_driver(udc, driver);
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<strong class="hl-keyword">if</strong> (ret != -EPROBE_DEFER)
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<em class="hl-comment">/* (2.3) Driver Match 成功后，从 pending 链表删除 */</em>
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list_del_init(&driver->pending);
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<strong class="hl-keyword">break</strong>;
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}
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<strong class="hl-keyword">return</strong> ret;
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}
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</pre></div>
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</li><li class="- topic/li li" data-ofbid="d354177e68__20250121172132">
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<div class="- topic/p p" data-ofbid="d354177e70__20250121172132">在 Gadget Driver 创建时，首先尝试和 <code class="+ topic/ph pr-d/codeph ph codeph">udc_list</code> 链表中的 Device 进行
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match()，match() 不成功则把 Driver 加入到 <code class="+ topic/ph pr-d/codeph ph codeph">gadget_driver_pending_list</code>
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链表中:<pre class="+ topic/pre pr-d/codeblock pre codeblock language-c" id="usb_gadget_bus__pre_j3c_5qz_21c" data-ofbid="usb_gadget_bus__pre_j3c_5qz_21c">gadget_dev_desc_UDC_store() → usb_gadget_probe_driver():
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<strong class="hl-keyword">int</strong> usb_gadget_probe_driver(<strong class="hl-keyword">struct</strong> usb_gadget_driver *driver)
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{
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<strong class="hl-keyword">struct</strong> usb_udc *udc = NULL;
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<strong class="hl-keyword">int</strong> ret = -ENODEV;
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<strong class="hl-keyword">if</strong> (!driver || !driver->bind || !driver->setup)
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<strong class="hl-keyword">return</strong> -EINVAL;
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mutex_lock(&udc_lock);
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<em class="hl-comment">/* (1.1) 如果 Driver 有 udc_name，尝试和 udc_list 链表中 Device 的 Name 进行 match() */</em>
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<strong class="hl-keyword">if</strong> (driver->udc_name) {
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list_for_each_entry(udc, &udc_list, list) {
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ret = strcmp(driver->udc_name, dev_name(&udc->dev));
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<strong class="hl-keyword">if</strong> (!ret)
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<strong class="hl-keyword">break</strong>;
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}
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<strong class="hl-keyword">if</strong> (ret)
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ret = -ENODEV;
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<strong class="hl-keyword">else</strong> <strong class="hl-keyword">if</strong> (udc->driver)
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ret = -EBUSY;
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<strong class="hl-keyword">else</strong>
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<strong class="hl-keyword">goto</strong> found;
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<em class="hl-comment">/* (1.2) 如果 Driver 没有 udc_name，尝试适配 udc_list 链表中第一个没有适配的 Device */</em>
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} <strong class="hl-keyword">else</strong> {
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list_for_each_entry(udc, &udc_list, list) {
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<em class="hl-comment">/* For now we take the first one */</em>
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<strong class="hl-keyword">if</strong> (!udc->driver)
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<strong class="hl-keyword">goto</strong> found;
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}
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}
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<strong class="hl-keyword">if</strong> (!driver->match_existing_only) {
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<em class="hl-comment">/* (2) 如果没有 match() 成功，则把 Driver 加入到 pending 链表 */</em>
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list_add_tail(&driver->pending, &gadget_driver_pending_list);
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pr_info(<span class="hl-string">"udc-core: couldn't find an available UDC - added [%s] to list of pending drivers\n"</span>,
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driver->function);
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ret = <span class="hl-number">0</span>;
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}
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mutex_unlock(&udc_lock);
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<strong class="hl-keyword">if</strong> (ret)
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pr_warn(<span class="hl-string">"udc-core: couldn't find an available UDC or it's busy\n"</span>);
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<strong class="hl-keyword">return</strong> ret;
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found:
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<em class="hl-comment">/* (3) 如果 Match 成功，对 Device 和 Driver 进行 bind() */</em>
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ret = udc_bind_to_driver(udc, driver);
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mutex_unlock(&udc_lock);
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<strong class="hl-keyword">return</strong> ret;
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||
}
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</pre></div>
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</li><li class="- topic/li li" data-ofbid="d354177e81__20250121172132">
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<div class="- topic/p p" data-ofbid="d354177e83__20250121172132">在 Device 和 Driver Match 成功时的 bind()
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动作：<pre class="+ topic/pre pr-d/codeblock pre codeblock language-c" id="usb_gadget_bus__codeblock_f2s_vqz_21c" data-ofbid="usb_gadget_bus__codeblock_f2s_vqz_21c"><strong class="hl-keyword">static</strong> <strong class="hl-keyword">int</strong> udc_bind_to_driver(<strong class="hl-keyword">struct</strong> usb_udc *udc, <strong class="hl-keyword">struct</strong> usb_gadget_driver *driver)
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{
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<strong class="hl-keyword">int</strong> ret;
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dev_dbg(&udc->dev, <span class="hl-string">"registering UDC driver [%s]\n"</span>,
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driver->function);
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<em class="hl-comment">/* (1) 数据成员的赋值 */</em>
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udc->driver = driver;
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udc->dev.driver = &driver->driver;
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udc->gadget->dev.driver = &driver->driver;
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usb_gadget_udc_set_speed(udc, driver->max_speed);
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||
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<em class="hl-comment">/* (2) 调用 Gadget Driver 的 bind() 函数 */</em>
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ret = driver->bind(udc->gadget, driver);
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||
<strong class="hl-keyword">if</strong> (ret)
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||
<strong class="hl-keyword">goto</strong> err1;
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||
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<em class="hl-comment">/* (3) 调用 Gadget Device 的 start() 函数
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udc->gadget->ops->udc_start(udc->gadget, udc->driver);
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*/</em>
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||
ret = usb_gadget_udc_start(udc);
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<strong class="hl-keyword">if</strong> (ret) {
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||
driver->unbind(udc->gadget);
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||
<strong class="hl-keyword">goto</strong> err1;
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||
}
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||
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<em class="hl-comment">/* (4) 调用 Gadget Device 的 pullup() 函数
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||
gadget->ops->pullup(gadget, 1/0);
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||
*/</em>
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usb_udc_connect_control(udc);
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||
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||
kobject_uevent(&udc->dev.kobj, KOBJ_CHANGE);
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<strong class="hl-keyword">return</strong> <span class="hl-number">0</span>;
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||
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||
}</pre></div>
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||
</li></ul><div class="- topic/p p" data-ofbid="d354177e88__20250121172132">
|
||
<div class="- topic/note note note note_note" id="usb_gadget_bus__note_cqy_ktn_y1c" data-ofbid="usb_gadget_bus__note_cqy_ktn_y1c"><span class="note__title">注：</span> 这里和一般的 Device 和 Driver 的适配规则有些不一样。一般的规则是一个 Dirver 可以适配多个
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||
Device，而一个 Device 只能适配一个 Driver。而这里的规则是一个 Gadget Device 只能适配一个 Gadget Driver，而一个
|
||
Gadget Driver 只能适配一个 Gadget Device。 Gadget Driver 代表的是一个 <code class="+ topic/ph pr-d/codeph ph codeph">Composite
|
||
Device</code>。</div>
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