详解linux 摄像头驱动编写
<p>对于现代嵌入式设备，特别是手机来说，摄像头是很重要的一个设备。很多同学买手机，一看颜值，第二就看摄像头拍照如何。所以，从某个角度来说，摄像头是各个厂家主打的应用功能。那么，linux是如何支持摄像头的，我们可以来看一下？</p>
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1、代码目录地址</p>
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<code class="plain plain">drivers/media</code>
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2、v4l2框架</p>
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目前linux上的camera都是按照v4l2框架来设计，它的地址位于drivers/media/v4l2-core</p>
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3、查看三星soc是如何支持camera的，可以查看drviers/media/platform/Kconfig</p>
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<code class="plain plain">config VIDEO_S3C_CAMIF </code>
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<code class="plain spaces"> </code><code class="plain plain">tristate "Samsung S3C24XX/S3C64XX SoC Camera Interface driver" </code>
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<code class="plain spaces"> </code><code class="plain plain">depends on VIDEO_V4L2 && I2C && VIDEO_V4L2_SUBDEV_API </code>
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<code class="plain spaces"> </code><code class="plain plain">depends on PM </code>
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<code class="plain spaces"> </code><code class="plain plain">depends on ARCH_S3C64XX || PLAT_S3C24XX || COMPILE_TEST </code>
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<code class="plain spaces"> </code><code class="plain plain">depends on HAS_DMA </code>
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<code class="plain spaces"> </code><code class="plain plain">select VIDEOBUF2_DMA_CONTIG </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">This is a v4l2 driver for s3c24xx and s3c64xx SoC series camera </code>
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<code class="plain spaces"> </code><code class="plain plain">host interface (CAMIF). </code>
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<code class="plain spaces"> </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 s3c-camif. </code>
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4、从Kconfig确认除了VIDEO_V4L2和VIDEO_V4L2_SUBDEV_API之外，它只依赖自己的目录</p>
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<code class="plain plain">obj-$(CONFIG_VIDEO_S3C_CAMIF) += s3c-camif/</code>
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5、继续查看s3c-camif目录的代码结构</p>
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<code class="plain plain"># Makefile for s3c244x/s3c64xx CAMIF driver </code>
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<code class="plain spaces"> </code>
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<code class="plain plain">s3c-camif-objs := camif-core.o camif-capture.o camif-regs.o </code>
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<code class="plain spaces"> </code>
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<code class="plain plain">obj-$(CONFIG_VIDEO_S3C_CAMIF) += s3c-camif.o</code>
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6、Makefile说的很清楚，它主要依赖camif-*.c三个文件</p>
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通过阅读，确认camif-core.c是注册文件</p>
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camif-regs.c是寄存器读写文件</p>
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camif-capture.c是主要的操作文件、接口文件</p>
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7、确认v4l2的函数操作接口</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">v4l2_ioctl_ops s3c_camif_ioctl_ops = { </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_querycap = s3c_camif_vidioc_querycap, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_enum_input = s3c_camif_vidioc_enum_input, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_g_input = s3c_camif_vidioc_g_input, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_s_input = s3c_camif_vidioc_s_input, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_enum_fmt_vid_cap = s3c_camif_vidioc_enum_fmt, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_try_fmt_vid_cap = s3c_camif_vidioc_try_fmt, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_s_fmt_vid_cap = s3c_camif_vidioc_s_fmt, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_g_fmt_vid_cap = s3c_camif_vidioc_g_fmt, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_g_selection = s3c_camif_g_selection, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_s_selection = s3c_camif_s_selection, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_reqbufs = s3c_camif_reqbufs, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_querybuf = s3c_camif_querybuf, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_prepare_buf = s3c_camif_prepare_buf, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_create_bufs = s3c_camif_create_bufs, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_qbuf = s3c_camif_qbuf, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_dqbuf = s3c_camif_dqbuf, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_streamon = s3c_camif_streamon, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_streamoff = s3c_camif_streamoff, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_subscribe_event = v4l2_ctrl_subscribe_event, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_unsubscribe_event = v4l2_event_unsubscribe, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.vidioc_log_status = v4l2_ctrl_log_status, </code>
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<code class="cpp plain">}; </code>
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<p>
and</p>
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<code class="cpp plain">649 </code><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">v4l2_file_operations s3c_camif_fops = { </code>
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<code class="cpp plain">650 .owner = THIS_MODULE, </code>
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<code class="cpp plain">651 .open = s3c_camif_open, </code>
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<code class="cpp plain">652 .release = s3c_camif_close, </code>
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<code class="cpp plain">653 .poll = s3c_camif_poll, </code>
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<code class="cpp plain">654 .unlocked_ioctl = video_ioctl2, </code>
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<code class="cpp plain">655 .mmap = s3c_camif_mmap, </code>
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<code class="cpp plain">656 };</code>
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<p>
8、和sd一样，接口比较简单，但是要深入了解camera，v4l2是绕不过去的。</p>
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这一点和sd卡、usb、asoc是一样的。</p>
<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/79850268</p>
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