设备进行EMI静电测试时，LCD显示屏异常之后不能恢复，需要在软件上检测LCD是否处于工作状态，如果没有处于工作状态，则需要重启LCD。

如何确定LCD是否处于工作状态？

参照SDK docs/Common/DISPLAY路径下的Rockchip_DRM_Panel_Porting_Guide_V1.6_20190228.pdf》文档，其中3.4章节提到了如何判断MIPI-DSI外设有正常工作？瑞芯微也为此申请了专利。

drivers/gpu/drm/drm_mipi_dsi.c

kernel/include/drm/drm_mipi_dsi.h

提供了对 MIPI-DSI 外设通信的相关 API。

支持 DCS 标准 MIPI_DCS_GET_POWER_MODE(0x0A)命令的外设,可以通过读取 power_mode 来判断，函数mipi_dsi_dcs_get_power_mode() - query the display module's current power mode。mode=0x08 说 明 设 备 目 前 是 OFF 状 态，mode=0x9c,说明设备目前是 ON 状态。

驱动说明文档

# echo off > /sys/class/drm/card0-DSI-1/status
# echo on > /sys/class/drm/card0-DSI-1/status

修改驱动，启动时获取power_mode

..\x3566_linux_v1.2.0\kernel\drivers\gpu\drm\panel\panel-simple.c文件，在static int panel_simple_dsi_probe(struct mipi_dsi_device *dsi)函数中增加读取液晶状态的函数：

static int panel_simple_dsi_probe(struct mipi_dsi_device *dsi)
{struct panel_simple *panel;struct device *dev = &dsi->dev;const struct panel_desc_dsi *desc;struct panel_desc_dsi *d;const struct of_device_id *id;int err;u8 mode;id = of_match_node(dsi_of_match, dsi->dev.of_node);if (!id)return -ENODEV;dev_info(dev, "panel_simple_dsi_probe\n");if (!id->data) {d = devm_kzalloc(dev, sizeof(*d), GFP_KERNEL);if (!d)return -ENOMEM;err = panel_simple_dsi_of_get_desc_data(dev, d);if (err) {dev_err(dev, "failed to get desc data: %d\n", err);return err;}}desc = id->data ? id->data : d;err = panel_simple_probe(&dsi->dev, &desc->desc);if (err < 0)return err;panel = dev_get_drvdata(dev);panel->dsi = dsi;dsi->mode_flags = desc->flags;dsi->format = desc->format;dsi->lanes = desc->lanes;++	/* user add begin */
++	if(dsi)
++	{
++		err = mipi_dsi_dcs_get_power_mode( dsi, &mode);
++		dev_info( dev, "get_power_mode err=%d, mode=%02x\n", err, mode );
++	}
++	/* user add end */err = mipi_dsi_attach(dsi);if (err) {struct panel_simple *panel = dev_get_drvdata(&dsi->dev);drm_panel_remove(&panel->base);}return err;
}

启动时没有连接屏幕，打印如下：

[root@RK356X:/]# dmesg | grep get_power_mode
[    0.267272] panel-simple-dsi fe060000.dsi.0: get_power_mode err=-110, mode=02

启动时连接了屏幕，打印如下：

[root@RK356X:/]# dmesg | grep get_power_mode
[    0.268318] panel-simple-dsi fe060000.dsi.0: get_power_mode err=0, mode=9c

 设备运行过程中定时查询屏幕状态

在panel-simple.c文件中增加一个内核线程函数，每5s读取一次power_mode：

static int kthread_checkLCDstatus_func(void * data)
{struct mipi_dsi_device *dsi = (struct mipi_dsi_device *)data;int err;u8 mode;while (!kthread_should_stop()) {	err = mipi_dsi_dcs_get_power_mode( dsi, &mode);dev_info( &dsi->dev, "get_power_mode err=%d, mode=%02x\n", err, mode );	msleep(5000);}return 0;
}

在panel_simple_dsi_probe()函数中创建并运行checkLCDstatus_kthread线程:

static struct task_struct *checkLCDstatus_kthread = NULL;static int panel_simple_dsi_probe(struct mipi_dsi_device *dsi)
{struct panel_simple *panel;struct device *dev = &dsi->dev;const struct panel_desc_dsi *desc;struct panel_desc_dsi *d;const struct of_device_id *id;int err;u8 mode;id = of_match_node(dsi_of_match, dsi->dev.of_node);if (!id)return -ENODEV;if (!id->data) {d = devm_kzalloc(dev, sizeof(*d), GFP_KERNEL);if (!d)return -ENOMEM;err = panel_simple_dsi_of_get_desc_data(dev, d);if (err) {dev_err(dev, "failed to get desc data: %d\n", err);return err;}}desc = id->data ? id->data : d;err = panel_simple_probe(&dsi->dev, &desc->desc);if (err < 0)return err;panel = dev_get_drvdata(dev);panel->dsi = dsi;dsi->mode_flags = desc->flags;dsi->format = desc->format;dsi->lanes = desc->lanes;++	/* user add begin */
++	if(dsi)
++	{
++		err = mipi_dsi_dcs_get_power_mode( dsi, &mode);
++		dev_info( dev, "get_power_mode err=%d, mode=%02x\n", err, mode );++		checkLCDstatus_kthread = kthread_run(kthread_checkLCDstatus_func, dsi, "test_task");
++	}
++	/* user add end */err = mipi_dsi_attach(dsi);if (err) {struct panel_simple *panel = dev_get_drvdata(&dsi->dev);drm_panel_remove(&panel->base);}return err;
}

设备运行过程中，手动复位触发LCD复位，读取的mode重9c变为了08，日志如下： 

[  118.415228] kthread is running
[  118.418300] panel-simple-dsi fe060000.dsi.0: get_power_mode err=0, mode=9c
[  123.535187] kthread is running
[  123.541131] panel-simple-dsi fe060000.dsi.0: get_power_mode err=0, mode=9c
[  128.655245] kthread is running
[  128.664003] panel-simple-dsi fe060000.dsi.0: get_power_mode err=0, mode=08
[  133.775156] kthread is running
[  133.786790] panel-simple-dsi fe060000.dsi.0: get_power_mode err=0, mode=08

设备运行过程中读取到power_mode为OFF状态时，重启内核

本应该只重启LCD即可，但没有合适的方法，所以直接重启系统，修改kthread_checkLCDstatus_func()函数：

static int kthread_checkLCDstatus_func(void * data)
{struct mipi_dsi_device *dsi = (struct mipi_dsi_device *)data;int err;u8 mode;while (!kthread_should_stop()) {	err = mipi_dsi_dcs_get_power_mode( dsi, &mode);dev_info( &dsi->dev, "get_power_mode err=%d, mode=%02x\n", err, mode );	msleep(5000);printk("panel-simple restart kernel\n");kernel_restart(NULL);					//linux kernel restart.}return 0;
}

方法不完善，请有这方面经验的朋友指教。