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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/boot/uboot-load-env-variables.dita">Edit online</a></span><h1 class="- topic/title title topictitle1" id="ariaid-title1">环境变量加载</h1><div class="date inPage">4 Dec 2024</div><div style="color: gray;">
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Read time: 2 minute(s)
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</div><div class="- topic/body concept/conbody body conbody"><div class="- topic/p p" data-ofbid="d132916e22__20250121171606">
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<div class="- topic/div div">
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<p class="- topic/p p" data-ofbid="d132916e26__20250121171606">如前面所述，环境变量的处理有两个阶段：</p>
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<ol class="- topic/ol ol" id="concept_tyf_bm3_pzb__ol_vng_wbh_bzb" data-ofbid="concept_tyf_bm3_pzb__ol_vng_wbh_bzb"><li class="- topic/li li" data-ofbid="d132916e30__20250121171606">
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<p class="- topic/p p" data-ofbid="d132916e32__20250121171606">环境变量初始</p>
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</li><li class="- topic/li li" data-ofbid="d132916e35__20250121171606">
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<p class="- topic/p p" data-ofbid="d132916e37__20250121171606">环境变量读取</p>
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</li></ol>
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<div class="- topic/p p" data-ofbid="d132916e41__20250121171606">如下面的调用流程， <span class="+ topic/keyword pr-d/apiname keyword apiname">env_init()</span> 在 <span class="+ topic/keyword pr-d/apiname keyword apiname">board_init_f()</span>
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阶段执行，但具体的加载过程 在 <span class="+ topic/keyword pr-d/apiname keyword apiname">board_init_r()</span>
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阶段执行。<pre class="+ topic/pre pr-d/codeblock pre codeblock language-c" id="concept_tyf_bm3_pzb__codeblock_fkq_nmr_c1c" data-ofbid="concept_tyf_bm3_pzb__codeblock_fkq_nmr_c1c">reset <em class="hl-comment">// arch/riscv/cpu/start.S</em>
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|-> save_boot_params <em class="hl-comment">// arch/riscv/mach-artinchip/lowlevel_init.S</em>
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|-> ...
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|-> board_init_f(); <em class="hl-comment">// common/board_f.c</em>
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|-> setup_reloc(); <em class="hl-comment">// common/board_f.c</em>
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|-> jump_to_copy(); <em class="hl-comment">// common/board_f.c</em>
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|-> relocate_code(); <em class="hl-comment">// arch/riscv/cpu/start.S</em>
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|-> invalidate_icache_all()
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|-> flush_dcache_all()
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|-> board_init_r();
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| <em class="hl-comment">// 逐个调用 init_sequence_r 里面的函数，其中包括 initr_env</em>
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|-> initr_env(); <em class="hl-comment">// common/board_r.c</em>
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|-> should_load_env(<strong class="hl-keyword">void</strong>);<em class="hl-comment">// common/board_r.c</em>
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| <em class="hl-comment">// 由于没有在 DTS 中进行配置，总是返回 1</em>
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| <em class="hl-comment">// fdtdec_get_config_int(gd->fdt_blob, "load-environment", 1);</em>
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|-> env_relocate(); <em class="hl-comment">// env/common.c</em>
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|-> env_load(); <em class="hl-comment">// env/env.c</em></pre></div>
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<p class="- topic/p p" data-ofbid="d132916e55__20250121171606">U-Boot 支持在多种存储介质中保存环境变量，并且提供了一个插拔式的机制，用于实现从 不同的存储介质中加载环境变量内容。</p>
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<div class="- topic/p p" data-ofbid="d132916e58__20250121171606">在添加新的环境变量加载器时，只需要实现对应存储介质的 <span class="+ topic/keyword pr-d/apiname keyword apiname">load</span> 和 <span class="+ topic/keyword pr-d/apiname keyword apiname">save</span> 函数，
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然后通过宏 <span class="+ topic/keyword pr-d/apiname keyword apiname">U_BOOT_ENV_LOCATION</span> 将对应的信息添加到
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<code class="+ topic/ph pr-d/codeph ph codeph">.u_boot_list_2</code> 链接段中。 比如下面的定义，将生成
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<code class="+ topic/ph pr-d/codeph ph codeph">.u_boot_list_2_env_driver_2_spinand</code>
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信息。<pre class="+ topic/pre pr-d/codeblock pre codeblock language-c" id="concept_tyf_bm3_pzb__codeblock_djh_4mr_c1c" data-ofbid="concept_tyf_bm3_pzb__codeblock_djh_4mr_c1c">U_BOOT_ENV_LOCATION(spinand) = {
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.location = ENVL_SPINAND,
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ENV_NAME(<span class="hl-string">"SPINAND"</span>)
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.load = env_spinand_load,
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#<strong class="hl-keyword">if</strong> defined(CMD_SAVEENV)
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.save = env_save_ptr(env_spinand_save),
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#endif
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};</pre></div>
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<div class="- topic/p p" data-ofbid="d132916e80__20250121171606"><span class="+ topic/keyword pr-d/apiname keyword apiname">env_driver_lookup()</span> 函数首先通过检查当前的启动设备，然后从
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<code class="+ topic/ph pr-d/codeph ph codeph">.u_boot_list_2</code> 段中查找对应启动设备的 ENV
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加载驱动，最后调用对应的驱动读取并导入环境变量内容。<pre class="+ topic/pre pr-d/codeblock pre codeblock language-c" id="concept_tyf_bm3_pzb__codeblock_jd5_4mr_c1c" data-ofbid="concept_tyf_bm3_pzb__codeblock_jd5_4mr_c1c">env_load(); <em class="hl-comment">// env/env.c</em>
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|-> env_driver_lookup(ENVOP_LOAD, prio);
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| |-> loc = env_get_location(); <em class="hl-comment">// board/artinchip/d211/env_location.c</em>
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| | |-> bd = aic_get_boot_device(); <em class="hl-comment">// 获取当前的启动设备</em>
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| |
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| |-> _env_driver_lookup(loc);
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| |-> drv = ll_entry_start();
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| <em class="hl-comment">// 查找指定存储介质的 env 加载驱动</em>
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|-> drv->load();
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<em class="hl-comment">// 此处调用个存储介质的对应函数</em>
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env_ram_load(); <em class="hl-comment">// board/artinchip/d211/env_location.c</em>
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env_spinand_load(); <em class="hl-comment">// env/spinand.c</em>
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env_sf_load(); <em class="hl-comment">// env/sf.c</em>
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env_mmc_load(); <em class="hl-comment">// env/mmc.c</em></pre></div>
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<p class="- topic/p p" data-ofbid="d132916e90__20250121171606">具体各种存储介质中，环境变量保存的位置可参考<a xml:lang="zh-CN" lang="zh-CN" class="- topic/xref xref" href="save-env-variable-on-memory-medium.html">存储介质上的保存</a>。</p>
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