详解linux pwm驱动编写

声学發表於 2023-6-10 00:00:00

<p>
pwm方波可以用来控制很多的设备，比如它可以被用来控制电机。简单来说，就是单位时间内的方波越多，那么电机的转速就会越快；反之就越慢。通过这个特性，soc就可以轻松地利用pwm对外设进行自动控制。所以，今天的主题就是pwm驱动。</p>
<p>
<strong>1、驱动目录</strong></p>
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<code class="plain plain">drivers/pwm</code>
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2、查看对应目录下的Kconfig</p>
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<code class="plain plain">config PWM_SAMSUNG</code>
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<code class="plain spaces"> </code><code class="plain plain">tristate "Samsung PWM support"</code>
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<code class="plain spaces"> </code><code class="plain plain">depends on PLAT_SAMSUNG || ARCH_EXYNOS</code>
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<code class="plain spaces"> </code><code class="plain plain">help</code>
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<code class="plain spaces">  </code><code class="plain plain">Generic PWM framework driver for Samsung.</code>
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<code class="plain spaces">  </code><code class="plain plain">To compile this driver as a module, choose M here: the module</code>
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<code class="plain spaces">  </code><code class="plain plain">will be called pwm-samsung.</code>
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3、确认PWM_SAMSUNG只依赖于自己之外，继续看Makefile</p>
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<code class="plain plain">obj-$(CONFIG_PWM) += core.o</code>
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<code class="plain plain">obj-$(CONFIG_PWM_SAMSUNG) += pwm-samsung.o</code>
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4、根据Makefile查阅pwm-samsung.c文件，结构比较清楚</p>
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<code class="cpp keyword bold">static</code> <code class="cpp keyword bold">struct</code> <code class="cpp plain">platform_driver pwm_samsung_driver = {</code>
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<code class="cpp spaces"> </code><code class="cpp plain">.driver = {</code>
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<code class="cpp spaces"> </code><code class="cpp plain">.name = </code><code class="cpp string">"samsung-pwm"</code><code class="cpp plain">,</code>
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<code class="cpp spaces"> </code><code class="cpp plain">.pm = &pwm_samsung_pm_ops,</code>
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<code class="cpp spaces"> </code><code class="cpp plain">.of_match_table = of_match_ptr(samsung_pwm_matches),</code>
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<code class="cpp spaces"> </code><code class="cpp plain">},</code>
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<code class="cpp spaces"> </code><code class="cpp plain">.probe = pwm_samsung_probe,</code>
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<code class="cpp spaces"> </code><code class="cpp plain">.</code><code class="cpp functions bold">remove</code> <code class="cpp plain">= pwm_samsung_remove,</code>
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<code class="cpp plain">};</code>
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<code class="cpp plain">module_platform_driver(pwm_samsung_driver);</code>
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5、soc设备大多数是platform设备，继续寻找probe函数中的有用信息</p>
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<code class="cpp plain">ret = pwmchip_add(&chip->chip);</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">(ret < 0) {</code>
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<code class="cpp spaces"> </code><code class="cpp plain">dev_err(dev, </code><code class="cpp string">"failed to register PWM chip\n"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp plain">clk_disable_unprepare(chip->base_clk);</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">ret;</code>
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<code class="cpp spaces"> </code><code class="cpp plain">}</code>
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6、找到注册函数后，接续看看函数接口点在什么地方</p>
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<code class="cpp keyword bold">static</code> <code class="cpp keyword bold">const</code> <code class="cpp keyword bold">struct</code> <code class="cpp plain">pwm_ops pwm_samsung_ops = {</code>
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<code class="cpp spaces"> </code><code class="cpp plain">.request = pwm_samsung_request,</code>
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<code class="cpp spaces"> </code><code class="cpp plain">.</code><code class="cpp functions bold">free</code> <code class="cpp plain">= pwm_samsung_free,</code>
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<code class="cpp spaces"> </code><code class="cpp plain">.enable = pwm_samsung_enable,</code>
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<code class="cpp spaces"> </code><code class="cpp plain">.disable = pwm_samsung_disable,</code>
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<code class="cpp spaces"> </code><code class="cpp plain">.config = pwm_samsung_config,</code>
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<code class="cpp spaces"> </code><code class="cpp plain">.set_polarity = pwm_samsung_set_polarity,</code>
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<code class="cpp spaces"> </code><code class="cpp plain">.owner = THIS_MODULE,</code>
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<code class="cpp plain">};</code>
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<p>
7、pwm设备没有中断函数，一般是立马生效，除此之外，代码中还是有设备树的内容，可以看看</p>
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<code class="cpp keyword bold">static</code> <code class="cpp keyword bold">const</code> <code class="cpp keyword bold">struct</code> <code class="cpp plain">of_device_id samsung_pwm_matches[] = {</code>
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<code class="cpp spaces"> </code><code class="cpp plain">{ .compatible = </code><code class="cpp string">"samsung,s3c2410-pwm"</code><code class="cpp plain">, .data = &s3c24xx_variant },</code>
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<code class="cpp spaces"> </code><code class="cpp plain">{ .compatible = </code><code class="cpp string">"samsung,s3c6400-pwm"</code><code class="cpp plain">, .data = &s3c64xx_variant },</code>
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<code class="cpp spaces"> </code><code class="cpp plain">{ .compatible = </code><code class="cpp string">"samsung,s5p6440-pwm"</code><code class="cpp plain">, .data = &s5p64x0_variant },</code>
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<code class="cpp spaces"> </code><code class="cpp plain">{ .compatible = </code><code class="cpp string">"samsung,s5pc100-pwm"</code><code class="cpp plain">, .data = &s5pc100_variant },</code>
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<code class="cpp spaces"> </code><code class="cpp plain">{ .compatible = </code><code class="cpp string">"samsung,exynos4210-pwm"</code><code class="cpp plain">, .data = &s5p64x0_variant },</code>
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<code class="cpp spaces"> </code><code class="cpp plain">{},</code>
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<code class="cpp plain">};</code>
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<code class="cpp plain">MODULE_DEVICE_TABLE(of, samsung_pwm_matches);</code>
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<code class="cpp keyword bold">static</code> <code class="cpp color1 bold">int</code> <code class="cpp plain">pwm_samsung_parse_dt(</code><code class="cpp keyword bold">struct</code> <code class="cpp plain">samsung_pwm_chip *chip)</code>
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<code class="cpp plain">{</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">struct</code> <code class="cpp plain">device_node *np = chip->chip.dev->of_node;</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">const</code> <code class="cpp keyword bold">struct</code> <code class="cpp plain">of_device_id *match;</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">struct</code> <code class="cpp plain">property *prop;</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">const</code> <code class="cpp plain">__be32 *cur;</code>
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<code class="cpp spaces"> </code><code class="cpp plain">u32 val;</code>
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<code class="cpp spaces"> </code><code class="cpp plain">match = of_match_node(samsung_pwm_matches, np);</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">(!match)</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">-ENODEV;</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">memcpy</code><code class="cpp plain">(&chip->variant, match->data, </code><code class="cpp keyword bold">sizeof</code><code class="cpp plain">(chip->variant));</code>
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<code class="cpp spaces"> </code><code class="cpp plain">of_property_for_each_u32(np, </code><code class="cpp string">"samsung,pwm-outputs"</code><code class="cpp plain">, prop, cur, val) {</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">(val >= SAMSUNG_PWM_NUM) {</code>
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<code class="cpp spaces">  </code><code class="cpp plain">dev_err(chip->chip.dev,</code>
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<code class="cpp spaces">  </code><code class="cpp string">"%s: invalid channel index in samsung,pwm-outputs property\n"</code><code class="cpp plain">,</code>
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<code class="cpp spaces">    </code><code class="cpp plain">__func__);</code>
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<code class="cpp spaces">  </code><code class="cpp keyword bold">continue</code><code class="cpp plain">;</code>
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<code class="cpp spaces"> </code><code class="cpp plain">}</code>
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<code class="cpp spaces"> </code><code class="cpp plain">chip->variant.output_mask |= BIT(val);</code>
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<code class="cpp spaces"> </code><code class="cpp plain">}</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">0;</code>
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<code class="cpp plain">}</code>
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<p>
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。</p>
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原文链接：https://blog.csdn.net/feixiaoxing/article/details/79889240</p>

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详解linux pwm驱动编写