TI AM335x kernel 4.4.12 LCD display 时钟翻转记录

因为公司硬件上已经确定LCD 转LVDS 转换芯片上确认以上升沿时钟为基准，所以只能在软件上调整相关东西。

入口在：

drivers/gpu/drm/tilcdc/tilcdc_drv.c入口函数：
module_init(tilcdc_drm_init);
出口函数：
module_exit(tilcdc_drm_fini);   722 static int __init tilcdc_drm_init(void)
723 {
724     DBG("init");
725     tilcdc_tfp410_init();
726     tilcdc_panel_init();   ---> 这里面有关监视器的初始化----------
727     return platform_driver_register(&tilcdc_platform_driver); |
728 }                                                             |                   |                   |
drivers/gpu/drm/tilcdc/tilcdc_panel.c                             ||
452 int __init tilcdc_panel_init(void)  <--------------------------
453 {
454     return platform_driver_register(&panel_driver);
455 }                                         |----------                                      |
437 static struct of_device_id panel_of_match[] = {     |
438         { .compatible = "ti,tilcdc,panel", },       |
439         { },                                        |
440 };                                                  |
441                                                     |
442 struct platform_driver panel_driver = { <------------
443     .probe = panel_probe,
444     .remove = panel_remove,
445     .driver = {
446         .owner = THIS_MODULE,
447         .name = "panel",
448         .of_match_table = panel_of_match,
449     },
450 };  

根据panel_of_match[].compatible = "ti,tilcdc,panel", 找到设备树相应内容。
arch/arm/boot/dts/am335x-chenfl.dts47     panel {48         compatible = "ti,tilcdc,panel";49         status = "okay";50         pinctrl-names = "default";51         pinctrl-0 = <&lcd_pins_s0>;52         panel-info {53             ac-bias           = <255>;54             ac-bias-intrpt    = <0>;55             dma-burst-sz      = <16>;56             bpp               = <16>;57             fdd               = <0x80>;58             sync-edge         = <0>;59             sync-ctrl         = <1>;60             raster-order      = <0>;61             fifo-th           = <0>;62             invert-pxl-clk    = <1>;63         };64 65         display-timings {66             native-mode = <&timing0>;67             timing0: 800x480 {68                 clock-frequency = <33260000>;69                 hactive = <800>;70                 vactive = <480>;71                 hfront-porch = <39>;72                 hback-porch = <39>;73                 hsync-len = <47>;74                 vback-porch = <29>;75                 vfront-porch = <13>;76                 vsync-len = <2>;77                 hsync-active = <1>;78                 vsync-active = <1>;79             };80         };81     };

确定平台设备与平台驱动已经相互匹配之后，我们可以直接跟踪驱动的probe
回到drivers/gpu/drm/tilcdc/tilcdc_panel.c
看到：442 struct platform_driver panel_driver = {
443     .probe = panel_probe,
444     .remove = panel_remove,
445     .driver = {
446         .owner = THIS_MODULE,
447         .name = "panel",
448         .of_match_table = panel_of_match,
449     },
450 };  panel_probe:
341 static int panel_probe(struct platform_device *pdev)
342 {
343     struct device_node *bl_node, *node = pdev->dev.of_node;
344     struct panel_module *panel_mod;
345     struct tilcdc_module *mod;
346     struct pinctrl *pinctrl;
347     int ret;
348     /* 如果没有设备树数据就直接跳出来 */
349     /* bail out early if no DT data: */
350     if (!node) {
351         dev_err(&pdev->dev, "device-tree data is missing\n");
352         return -ENXIO;
353     }
354
355     panel_mod = devm_kzalloc(&pdev->dev, sizeof(*panel_mod), GFP_KERNEL);
356     if (!panel_mod)
357         return -ENOMEM;
358
359     bl_node = of_parse_phandle(node, "backlight", 0);
360     if (bl_node) {
361         panel_mod->backlight = of_find_backlight_by_node(bl_node);
362         of_node_put(bl_node);
363
364         if (!panel_mod->backlight)
365             return -EPROBE_DEFER;
366
367         dev_info(&pdev->dev, "found backlight\n");
368     }
369
370     panel_mod->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable",
371                              GPIOD_OUT_LOW);
372     if (IS_ERR(panel_mod->enable_gpio)) {
373         ret = PTR_ERR(panel_mod->enable_gpio);
374         dev_err(&pdev->dev, "failed to request enable GPIO\n");
375         goto fail_backlight;
376     }
377
378     if (panel_mod->enable_gpio)
379         dev_info(&pdev->dev, "found enable GPIO\n");
380
381     mod = &panel_mod->base;
382     pdev->dev.platform_data = mod;
383
384     tilcdc_module_init(mod, "panel", &panel_module_ops);
385
386     pinctrl = devm_pinctrl_get_select_default(&pdev->dev);
387     if (IS_ERR(pinctrl))
388         dev_warn(&pdev->dev, "pins are not configured\n");
389     /*  对应时序的设置，和设备树中的display-timings 有关   */
390     panel_mod->timings = of_get_display_timings(node);
391     if (!panel_mod->timings) {
392         dev_err(&pdev->dev, "could not get panel timings\n");
393         ret = -EINVAL;
394         goto fail_free;
395     }
396      /*  对应的相关信息设置，跟panel-info 这个节点有关  */
397     panel_mod->info = of_get_panel_info(node);
398     if (!panel_mod->info) {
399         dev_err(&pdev->dev, "could not get panel info\n");
400         ret = -EINVAL;
401         goto fail_timings;
402     }
403
404     mod->preferred_bpp = panel_mod->info->bpp;
405
406     return 0;
407
408 fail_timings:
409     display_timings_release(panel_mod->timings);
410
411 fail_free:
412     tilcdc_module_cleanup(mod);
413
414 fail_backlight:
415     if (panel_mod->backlight)
416         put_device(&panel_mod->backlight->dev);
417     return ret;
418 }                                                                               /*  这是上面的 of_get_panel_info 传进来的 */
292 static struct tilcdc_panel_info *of_get_panel_info(struct device_node *np)
293 {
294     struct device_node *info_np;
295     struct tilcdc_panel_info *info;
296     int ret = 0;
297
298     if (!np) {
299         pr_err("%s: no devicenode given\n", __func__);
300         return NULL;
301     }
302
303     info_np = of_get_child_by_name(np, "panel-info");
304     if (!info_np) {
305         pr_err("%s: could not find panel-info node\n", __func__);
306         return NULL;
307     }
308
309     info = kzalloc(sizeof(*info), GFP_KERNEL);
310     if (!info) {
311         pr_err("%s: allocation failed\n", __func__);
312         of_node_put(info_np);
313         return NULL;
314     }
315     /*  这里我们可以看到，如果一个出错，ret 就会为真，这是上面的设备树的必需选项的配对  */
316     ret |= of_property_read_u32(info_np, "ac-bias", &info->ac_bias);
317     ret |= of_property_read_u32(info_np, "ac-bias-intrpt", &info->ac_bias_intrpt);
318     ret |= of_property_read_u32(info_np, "dma-burst-sz", &info->dma_burst_sz);
319     ret |= of_property_read_u32(info_np, "bpp", &info->bpp);
320     ret |= of_property_read_u32(info_np, "fdd", &info->fdd);
321     ret |= of_property_read_u32(info_np, "sync-edge", &info->sync_edge);
322     ret |= of_property_read_u32(info_np, "sync-ctrl", &info->sync_ctrl);
323     ret |= of_property_read_u32(info_np, "raster-order", &info->raster_order);
324     ret |= of_property_read_u32(info_np, "fifo-th", &info->fifo_th);
325
326     /* optional: */ /*  这是可选选项，下面第二个则是时钟反转的选项。在设备中添加一个选项即可。 */
327     info->tft_alt_mode      = of_property_read_bool(info_np, "tft-alt-mode");
328     info->invert_pxl_clk    = of_property_read_bool(info_np, "invert-pxl-clk");
329
330     if (ret) {
331         pr_err("%s: error reading panel-info properties\n", __func__);
332         kfree(info);
333         of_node_put(info_np);
334         return NULL;
335     }
336     of_node_put(info_np);
337
338     return info;
339 }   /*  设备树修改 */47     panel {                                                                     48         compatible = "ti,tilcdc,panel";                                         49         status = "okay";                                                        50         pinctrl-names = "default";                                              51         pinctrl-0 = <&lcd_pins_s0>;                                             52         panel-info {                                                            53             ac-bias           = <255>;                                          54             ac-bias-intrpt    = <0>;                                            55             dma-burst-sz      = <16>;                                           56             bpp               = <16>;                                           57             fdd               = <0x80>;                                         58             sync-edge         = <0>;                                            59             sync-ctrl         = <1>;                                            60             raster-order      = <0>;                                            61             fifo-th           = <0>;                                            62             invert-pxl-clk    = <1>;    /* 添加这个选项设置为1 */                                        63         };重新编译设备树，重新启动，看效果。