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<\/p>\nLCD is a commonly used peripheral, and semiconductor manufacturers typically provide pre-written LCD interface driver programs for their chips. Developers don’t need to modify the LCD driver section; they only need to adjust the device tree according to the specific LCD device they are using. While no modifications are necessary in the driver, it’s still essential to comprehend the LCD driver process.<\/p>\n
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In the Linux operating system, applications ultimately interact with the video memory of RGB LCD to display characters, images, and other information on the LCD screen. Memory management in Linux is rigorous, and video memory needs to be allocated. Moreover, because of the presence of virtual memory, the video memory set by the driver and the video memory accessed by the application must correspond to the same physical memory. To address this issue, the Framebuffer (referred to as “fb”) was introduced. The Framebuffer represents a memory area that stores a frame of an image. Writing data to this memory is equivalent to writing data to the screen. In essence, the Framebuffer maps each point on the screen to a linear memory space, enabling programs to change the value of this memory segment to alter the color of a specific point on the screen.<\/p>\n
The Framebuffer mechanism provides a unified interface for user space operations on display devices, abstracting away the differences between underlying hardware components. When the LCD driver is successfully loaded, it generates a device file named struct fb_info { #ifdef CONFIG_FB_BACKLIGHT The Linux kernel abstracts all Framebuffers as For a given chip, the driver code for the eLCDIF controller for LCD screens with different resolutions remains the same. As an example, let’s consider the LCD driver for the NXP IMX6ULL chip in Linux and briefly outline the LCD driver’s process.<\/p>\n lcdif: lcdif@021c8000 { static const struct of_device_id mxsfb_dt_ids[] = { module_platform_driver(mxsfb_driver);<\/p>\n static int mxsfb_probe(struct platform_device *pdev) { host = devm_kzalloc(&pdev->dev, sizeof(struct mxsfb_info), GFP_KERNEL); fb_info = framebuffer_alloc(sizeof(struct fb_info), &pdev->dev); ret = devm_request_irq(&pdev->dev, irq, mxsfb_irq_handler, 0, dev_name(&pdev->dev), host); host->base = devm_ioremap_resource(&pdev->dev, res); fb_info->pseudo_palette = devm_kzalloc(&pdev->dev, sizeof(u32) * 16, GFP_KERNEL); INIT_LIST_HEAD(&fb_info->modelist); ret = mxsfb_init_fbinfo(host); mxsfb_dispdrv_init(pdev, fb_info);<\/p>\n if (!host->dispdrv) { if (!host->enabled) { ret = register_framebuffer(fb_info); The primary tasks of the In fact, the use of the Linux system has always been a challenging technical aspect for many LCD module suppliers. Choosing the right LCD module supplier is not easy for those who develop products using the Linux system. RJOYTEK is a technology company that specializes in LCD modules and board development. If you need further technical support, please feel free to contact us<\/a>!<\/p>\n LCD is a commonly used peripheral, and semiconductor manufacturers typically provide pre-written LCD interface driver programs for their chips. Developers don’t need to modify the LCD driver section; they only need to adjust the device tree according to the specific LCD device they are using. While no modifications are necessary […]<\/p>\n","protected":false},"author":3,"featured_media":8381,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[429],"tags":[328,327],"class_list":["post-8379","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-touch-panel-basics","tag-lcd-screen-drivers","tag-linux"],"acf":[],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\/dev\/fbX<\/code>. Applications can access the LCD through this device file. \/dev\/fbX<\/code> is a character device, and it has its corresponding file_operations<\/code> operation set, which is defined in the drivers\/video\/fbdev\/core\/fbmem.c<\/code> file.<\/p>\n
\natomic_t count;
\nint node;
\nint flags;
\nstruct mutex lock;
\nstruct mutex mm_lock;
\nstruct fb_var_screeninfo var;
\nstruct fb_fix_screeninfo fix;
\nstruct fb_monspecs monspecs;
\nstruct work_struct queue;
\nstruct fb_pixmap pixmap;
\nstruct fb_pixmap sprite;
\nstruct fb_cmap cmap;
\nstruct list_head modelist;
\nstruct fb_videomode *mode;<\/p>\n
\nstruct backlight_device *bl_dev;
\nstruct mutex bl_curve_mutex;
\nu8 bl_curve[FB_BACKLIGHT_LEVELS];
\n#endif
\nstruct fb_ops *fbops;
\nstruct device *device;
\nstruct device *dev;
\nint class_flag;
\nchar __iomem *screen_base;
\nunsigned long screen_size;
\nvoid *pseudo_palette;
\n};<\/p>\n<\/div>\nfb_info<\/code> structures. The fb_info<\/code> structure contains the complete attributes and operation sets of the Framebuffer device. As a result, each Framebuffer device is associated with an fb_info<\/code>. The structure is defined in the include\/linux\/fb.h<\/code> file.<\/p>\n2. Analysis of the LCD Driver<\/h3>\n
\n
imx6ull.dtsi<\/code> file and locate the content of the lcdif<\/code> node, which contains configuration details for the LCD interface controller.<\/li>\n<\/ul>\n
\ncompatible = “fsl,imx6ul-lcdif”, “fsl,imx28-lcdif”;
\nreg = <0x021c8000 0x4000>;
\ninterrupts = <GIC_SPI 5 IRQ_TYPE_LEVEL_HIGH>;
\nclocks = <&clks IMX6UL_CLK_LCDIF_PIX>,
\n<&clks IMX6UL_CLK_LCDIF_APB>,
\n<&clks IMX6UL_CLK_DUMMY>;
\nclock-names = “pix”, “axi”, “disp_axi”;
\nstatus = “disabled”;
\n};<\/p>\n\n
compatible<\/code> property value is used to match the device driver in the Linux source code. The mxsfb.c<\/code> file contains the platform driver for the MXS Framebuffer.<\/li>\n<\/ul>\n
\n{ .compatible = “fsl,imx23-lcdif”, .data = &mxsfb_devtype[0], },
\n{ .compatible = “fsl,imx28-lcdif”, .data = &mxsfb_devtype[1], },
\n{ \/* sentinel *\/ }
\n};
\n……
\n……
\nstatic struct platform_driver mxsfb_driver = {
\n.probe = mxsfb_probe,
\n.remove = mxsfb_remove,
\n.shutdown = mxsfb_shutdown,
\n.id_table = mxsfb_devtype,
\n.driver = {
\n.name = DRIVER_NAME,
\n.of_match_table = mxsfb_dt_ids,
\n.pm = &mxsfb_pm_ops,
\n},
\n};<\/p>\n\n
mxsfb_probe<\/code> function is executed. This function initializes the Framebuffer device, allocates resources, maps memory, and sets up the interrupt handler.<\/li>\n<\/ul>\n
\nconst struct of_device_id *of_id = of_match_device(mxsfb_dt_ids, &pdev->dev);
\nstruct resource *res;
\nstruct mxsfb_info *host;
\nstruct fb_info *fb_info;
\nstruct pinctrl *pinctrl;
\nint irq = platform_get_irq(pdev, 0);
\nint gpio, ret;
\n……
\nres = platform_get_resource(pdev, IORESOURCE_MEM, 0);
\nif (!res) {
\ndev_err(&pdev->dev, “Cannot get memory IO resource\\n”);
\nreturn -ENODEV;
\n}<\/p>\n
\nif (!host) {
\ndev_err(&pdev->dev, “Failed to allocate IO resource\\n”);
\nreturn -ENOMEM;
\n}<\/p>\n
\nif (!fb_info) {
\ndev_err(&pdev->dev, “Failed to allocate fbdev\\n”);
\ndevm_kfree(&pdev->dev, host);
\nreturn -ENOMEM;
\n}
\nhost->fb_info = fb_info;
\nfb_info->par = host;<\/p>\n
\nif (ret) {
\ndev_err(&pdev->dev, “request_irq (%d) failed with error %d\\n”, irq, ret);
\nret = -ENODEV;
\ngoto fb_release;
\n}<\/p>\n
\nif (IS_ERR(host->base)) {
\ndev_err(&pdev->dev, “ioremap failed\\n”);
\nret = PTR_ERR(host->base);
\ngoto fb_release;
\n}
\n……<\/p>\n
\nif (!fb_info->pseudo_palette) {
\nret = -ENOMEM;
\ngoto fb_release;
\n}<\/p>\n
\npm_runtime_enable(&host->pdev->dev);<\/p>\n
\nif (ret != 0)
\ngoto fb_pm_runtime_disable;<\/p>\n
\npinctrl = devm_pinctrl_get_select_default(&pdev->dev);
\nif (IS_ERR(pinctrl)) {
\nret = PTR_ERR(pinctrl);
\ngoto fb_pm_runtime_disable;
\n}
\n}<\/p>\n
\nwritel(0, host->base + LCDC_CTRL);
\nmxsfb_set_par(fb_info);
\nmxsfb_enable_controller(fb_info);
\npm_runtime_get_sync(&host->pdev->dev);
\n}<\/p>\n
\nif (ret != 0) {
\ndev_err(&pdev->dev, “Failed to register framebuffer\\n”);
\ngoto fb_destroy;
\n}
\n……
\nreturn ret;
\n}<\/p>\n\n
mxsfb_probe<\/code> function include allocating memory for fb_info<\/code>, allocating memory for pseudo_palette<\/code>, initializing the eLCDIF controller, and registering the fb_info<\/code> with the Linux kernel.<\/p>\n\n