1、背景介绍
飞腾2000+芯片通过I2C连接一块RTC时钟芯片（BellingBL5372）来实现麒麟信安系统下后的守时功能。目前BIOS支持UEFI功能，BIOS上电后能获取RTC时间，并将时间写入相应的UEFI变量或内存区域，操作系统上电后使用UEFI的APIs来读取相应的RTC时间变量或内存区域。
2、问题描述
在低温情况下（-42度），发现BIOS有概率无法获取到RTC时间，导致写入UEFI变量写入失败，从而操作系统也无法获取正确时间，变成系统出厂时间（2019年9月3日），如下图为出错情况：
但其实RTC芯片是正常工作的，当恢复到常温后又能获取到正确的时间，如下图
问题表现为低温情况下RTC守时不准。
3、原因分析
上电时BIOS通过I2C去访问RTC时钟芯片，由于FT2000+芯片商业档工作范围为0-70度，在低温-42度情况下完全有可能工作不正常，尤其是刚上电的那十几秒内，此时的I2C有概率无法读到RTC时钟芯片，导致BIOS时间无法获取，进一步导致系统下守时失败。
解决RTC问题其实就是解决一个温度问题，确保在温度满足芯片工作范围的情况下去读取RTC时钟芯片，也就是将读取时间后移，让芯片工作一段时间温度达到0度后再去读取。
对系统来说，有两种获取RTC时间的方式，一种就是从BIOS UEFI空间中去获取，另一种是调用系统下的驱动直接去读取时间。明显第二种方法是在操作系统启动过程中了，读取时间后移，能确保读到正确的时间。
4、问题解决
明确了通过加载驱动来获取RTC时间，那就按照这个思路去实现即可。
首先，在BIOS中添加RTC设备，通过dtb的方式添加，如下：
&i2c0 {status = "ok";rtc@32 {compatible = "beilin,bl5372";reg = <0x32>;status = "ok";};
};这样驱动就能和设备匹配上，驱动代码如下：
/** An I2C driver for Beilin BL5372 RTC*/#include <linux/i2c.h>
#include <linux/bcd.h>
#include <linux/rtc.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/of.h>#define DEG 0#define DRV_VERSION "2.0"#define TIME24 0
#define RS5C_ADDR(R) (((R) << 4) | 0)
#define RS5C372_REG_SECS 0
#define RS5C372_REG_MINS 1
#define RS5C372_REG_HOURS 2
#define RS5C372_REG_WDAY 3
#define RS5C372_REG_DAY 4
#define RS5C372_REG_MONTH 5
#define RS5C372_REG_YEAR 6
#define RS5C372_REG_TRIM 7
#define RS5C_REG_ALARM_A_MIN 8 /* or ALARM_W */
#define RS5C_REG_ALARM_A_HOURS 9
#define RS5C_REG_ALARM_A_WDAY 10#define RS5C_REG_ALARM_B_MIN 11 /* or ALARM_D */
#define RS5C_REG_ALARM_B_HOURS 12
#define RS5C_REG_ALARM_B_WDAY 13 /* (ALARM_B only) */
#define RS5C_REG_CTRL1 14
#define RS5C_REG_CTRL2 15
#define DEVICE_ADDR 0x32 //0x5dstatic unsigned rs5c_reg2hr(unsigned reg)
{
#if TIME24printk("<RTC> TIME24 0x%x\n",bcd2bin(reg & 0x3f));return bcd2bin(reg & 0x3f);
#elseunsigned hour;printk("<RTC> TIME12 0x%x\n",bcd2bin(reg & 0x1f));hour = bcd2bin(reg & 0x1f);if (hour == 12)hour = 0;if (reg & 0x20)hour += 12;printk("<RTC> TIME12 hour=%d\n",hour);return hour;
#endif
}static unsigned rs5c_reg2mon(unsigned reg)
{
#if TIME24printk("<RTC> TIME24 0x%x\n",bcd2bin(reg & 0x3f));return bcd2bin(reg & 0x3f);
#elseunsigned month;printk("<RTC> TIME12 0x%x\n",bcd2bin(reg & 0x1f));month = bcd2bin(reg & 0x1f);if (month > 12)month -= 12;printk("<RTC> TIME12 hour=%d\n",month);return month;
#endif
}static unsigned rs5c_hr2reg(unsigned hour)
{#if TIME24printk("<RTC> TIME24 0x%x\n",bin2bcd(hour));return bin2bcd(hour);#elseif (hour > 12){printk("<RTC> TIME12(>12) 0x%x\n",(0x20 | bin2bcd(hour - 12)));return 0x20 | bin2bcd(hour - 12);}if (hour == 12){printk("<RTC> TIME12(==12) 0x%x\n",(0x20 | bin2bcd(12)));return 0x20 | bin2bcd(12);}if (hour == 0){printk("<RTC> TIME12(==0) 0x%x\n",bin2bcd(12));return bin2bcd(12);}printk("<RTC> TIME12(<12) 0x%x\n",bin2bcd(hour));return bin2bcd(hour);
#endif
}//-----------------------------------------------
static struct i2c_driver bl5372_driver;struct bl5372 {struct rtc_device *rtc;struct device *dev;int irq;/*unsigned char sec;unsigned char min;unsigned char hour;unsigned char week;unsigned char day;unsigned char month;unsigned int year;*/
};static int i2c_write_bytes(struct i2c_client *client, uint8_t *data, uint16_t len)
{struct i2c_msg msg;int ret=-1;msg.flags = !I2C_M_RD;msg.addr = client->addr;msg.len = len;msg.buf = data;ret=i2c_transfer(client->adapter, &msg,1);return ret;
}static int bl5372_get_datetime(struct i2c_client *client, struct rtc_time *tm)
{struct bl5372 *bl5372 = i2c_get_clientdata(client);unsigned char buf[7] = { RS5C_ADDR(RS5C372_REG_SECS) };printk("<RTC>bsl5372_get_datetime\n");struct i2c_msg msgs[] = {{/* setup read ptr */.addr = client->addr,.flags = 0,/* write */.len = 1,.buf = buf},{/* read the sec,min,hour,week,day,month,year */.addr = client->addr,.flags = I2C_M_RD,/* read */.len = 7,.buf = buf},};//int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)//@num: Number of messages to be executed.//ÕâÀïÓÐÁœžöÏûÏ¢£¬ msgs[]µÄŽóС/* read registers */if ((i2c_transfer(client->adapter, msgs, 2)) != 2) {dev_err(&client->dev, "%s: read error\n", __func__);return -EIO;}printk("<RTC> buf[2]=0x%x\n",buf[2]);tm->tm_sec = bcd2bin(buf[0] & 0x7f);tm->tm_min = bcd2bin(buf[1] & 0x7f);printk("<RTC> Get hour Label*****\n");tm->tm_hour = rs5c_reg2hr(buf[2]);tm->tm_mday = bcd2bin(buf[4] & 0x7f);tm->tm_wday = bcd2bin(buf[3] & 0x7f);printk("<RTC> Get month Label*****\n");//tm->tm_mon = rs5c_reg2hr(buf[5])-1;tm->tm_mon = rs5c_reg2mon(buf[5])-1;tm->tm_year = bcd2bin(buf[6] & 0x7f)+100;printk("<RTC>@GET1 year%d month%d mday%d wday%d hour%d min%d sec%d\n",tm->tm_year,tm->tm_mon,tm->tm_mday,tm->tm_wday,tm->tm_hour,tm->tm_min,tm->tm_sec);#if 1//------------------------------------buf[0]= RS5C_ADDR(RS5C_REG_CTRL2);struct i2c_msg msgs2[] = {{/* setup read */.addr = client->addr,.len = 1,.buf = buf},{/* read is_24hour */.addr = client->addr,.flags = I2C_M_RD,.len = 1,.buf = buf},};/* read registers */if ((i2c_transfer(client->adapter, msgs2, 2)) != 2) {dev_err(&client->dev, "%s: read error\n", __func__);return -EIO;}if(buf[0]&0x20){printk("24小时\n");tm->tm_hour= (tm->tm_hour<24)? (tm->tm_hour):(24-tm->tm_hour);}else{tm->tm_hour=(tm->tm_hour<24)? (tm->tm_hour):(tm->tm_hour+24);// tm->tm_mday=(tm->tm_mday<7)? (tm->tm_mday):(tm->tm_mday+8-24);// tm->tm_hour=tm->tm_hour+8;}#endif//tm->tm_hour= (tm->tm_hour<24)? (tm->tm_hour):(tm->tm_hour-24);/* the clock can give out invalid datetime, but we cannot return* -EINVAL otherwise hwclock will refuse to set the time on bootup.*/printk("<RTC>@GET2 year%d month%d mday%d wday%d hour%d min%d sec%d\n",tm->tm_year,tm->tm_mon,tm->tm_mday,tm->tm_wday,tm->tm_hour,tm->tm_min,tm->tm_sec);if (rtc_valid_tm(tm) < 0)dev_err(&client->dev, "retrieved date/time is not valid.\n");return 0;
}static int bl5372_set_datetime(struct i2c_client *client, struct rtc_time *tm)
{struct bl5372 *bl5372 = i2c_get_clientdata(client);int i, err;unsigned char buf[7];printk("<RTC>####bl5372_set_datetime\n");
//------------------------------------buf[0]= RS5C_ADDR(RS5C_REG_CTRL2);struct i2c_msg msgs2[] = {{/* setup read */.addr = client->addr,.len = 1,.buf = buf},{/* read is_24hour */.addr = client->addr,.flags = I2C_M_RD,.len = 1,.buf = buf},};/* read registers */if ((i2c_transfer(client->adapter, msgs2, 2)) != 2) {dev_err(&client->dev, "%s: read error\n", __func__);return -EIO;}/* if((buf[0]&0x20)== 0){printk("RTC 12xiaoshi\n");rs5c_hr2regbuf[0] |= (1<<5);err = i2c_master_send(client, buf, 1);}
*/printk("<RTC>IN####year%d month%d mday%d wday%d hour%d min%d sec%d\n",tm->tm_year,tm->tm_mon,tm->tm_mday,tm->tm_wday,tm->tm_hour,tm->tm_min,tm->tm_sec);//------------------------/* hours, minutes and seconds */buf[0] = bin2bcd(tm->tm_sec);buf[1] = bin2bcd(tm->tm_min);printk("<RTC> Set hour Label*****\n");buf[2] = rs5c_hr2reg(tm->tm_hour);buf[3] = bin2bcd(tm->tm_wday & 0x07); //week 0~6buf[4] = bin2bcd(tm->tm_mday);buf[5] = bin2bcd(tm->tm_mon)+1;// 0~11tm->tm_year -= 100;buf[6] = bin2bcd(tm->tm_year % 100);// start at 1900 2018=>118
//
printk("###########write data to rtc \n");for(i=0;i<7;i++)
{
printk("buf[%d] is 0x%x\n",i,buf[i]);
}err = i2c_smbus_write_byte_data(client, RS5C_ADDR(RS5C372_REG_SECS), buf[0]);i2c_smbus_write_byte_data(client, RS5C_ADDR(RS5C372_REG_MINS) , buf[1]);i2c_smbus_write_byte_data(client, RS5C_ADDR(RS5C372_REG_HOURS) , buf[2]);i2c_smbus_write_byte_data(client, RS5C_ADDR(RS5C372_REG_WDAY) , buf[3]);i2c_smbus_write_byte_data(client, RS5C_ADDR(RS5C372_REG_DAY) , buf[4]);i2c_smbus_write_byte_data(client, RS5C_ADDR(RS5C372_REG_MONTH) , buf[5]);i2c_smbus_write_byte_data(client, RS5C_ADDR(RS5C372_REG_YEAR) , buf[6]);return 0;
}#ifdef CONFIG_RTC_INTF_DEV
static int bl5372_rtc_ioctl(struct device *dev, unsigned int cmd, unsigned long arg)
{struct bl5372 *bl5372 = i2c_get_clientdata(to_i2c_client(dev));struct rtc_time tm;switch (cmd) {case RTC_RD_TIME://bl5372_get_datetime(to_i2c_client(dev), &tm);return 0;case RTC_SET_TIME:if (copy_from_user(&tm, arg, sizeof(tm)))return -EFAULT;bl5372_set_datetime(to_i2c_client(dev), &tm);return 0;default:return -ENOIOCTLCMD;}}
#else
#define bl5372_rtc_ioctl NULL
#endifstatic int bl5372_rtc_read_time(struct device *dev, struct rtc_time *tm)
{return bl5372_get_datetime(to_i2c_client(dev), tm);
}static int bl5372_rtc_set_time(struct device *dev, struct rtc_time *tm)
{return bl5372_set_datetime(to_i2c_client(dev), tm);
}static int bl5372_rtc_getalarm(struct device *dev, struct rtc_wkalrm *wkalrm)
{struct bl5372 *bl5372 = i2c_get_clientdata(to_i2c_client(dev));return 0;
}static int bl5372_rtc_setalarm(struct device *dev, struct rtc_wkalrm *wkalrm)
{struct bl5372 *bl5372 = i2c_get_clientdata(to_i2c_client(dev));return 0;
}static int bl5372_rtc_alarm_irq_enable(struct device *dev, unsigned int enabled)
{//struct bl5372 *bl5372 = dev_get_drvdata(dev);struct bl5372 *bl5372 = i2c_get_clientdata(to_i2c_client(dev));return 0;
}static const struct rtc_class_ops bl5372_rtc_ops = {.ioctl = bl5372_rtc_ioctl,.read_time = bl5372_rtc_read_time,.set_time = bl5372_rtc_set_time,.read_alarm = bl5372_rtc_getalarm,.set_alarm = bl5372_rtc_setalarm,.alarm_irq_enable = bl5372_rtc_alarm_irq_enable
};static int bl5372_probe(struct i2c_client *client,const struct i2c_device_id *id)
{struct bl5372 *bl5372;if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)){return -ENODEV;}bl5372 = devm_kzalloc(&client->dev, sizeof(struct bl5372),GFP_KERNEL);if (!bl5372){return -ENOMEM;}device_init_wakeup(&client->dev, 1);i2c_set_clientdata(client, bl5372);bl5372->rtc = devm_rtc_device_register(&client->dev,bl5372_driver.driver.name,&bl5372_rtc_ops, THIS_MODULE);if (IS_ERR(bl5372->rtc)){return PTR_ERR(bl5372->rtc);}bl5372->rtc->uie_unsupported = 1;return 0;
}static int bl5372_remove(struct i2c_client *client)
{return 0;
}static const struct i2c_device_id bl5372_id[] = {{ "bl5372", 0 },{ }
};
MODULE_DEVICE_TABLE(i2c, bl5372_id);#ifdef CONFIG_OF
static const struct of_device_id bl5372_of_match[] = {{ .compatible = "beilin,bl5372" },{}
};
MODULE_DEVICE_TABLE(of, bl5372_of_match);
#endifstatic struct i2c_driver bl5372_driver = {.driver = {.name = "rtc-bl5372",.owner = THIS_MODULE,.of_match_table = of_match_ptr(bl5372_of_match),},.probe = bl5372_probe,.remove = bl5372_remove,.id_table = bl5372_id,
};module_i2c_driver(bl5372_driver);MODULE_AUTHOR("Zhengweiqing <1548889230@qq.com>");
MODULE_DESCRIPTION("Beilin BL5372 RTC driver");
MODULE_LICENSE("GPL");
MODULE_VERSION(DRV_VERSION);
下面是Makefile
obj-m +=rtc_bl5372.oKDIR=/lib/modules/$(shell uname -r)/buildall:make -C $(KDIR) M=$(PWD) modules
clean:make -C $(KDIR) M=$(PWD) clean
编译成ko，然后包进内核里面
将驱动编到内核里面后重新上电能发现系统下面有两个rtc设备，其中rtc0是系统采用BIOS UEFI方式产生的，rtc1是系统加载驱动产生的，如下图
由于系统时间默认采用的是从rtc0获取的时间，需要改为从rtc1（通过加载驱动产生的设备）获取时间。
在/etc/udev/rules.d下创建文件，这里命名为rtc1.rules
文件内容如下：
KERNEL=="rtc0",SYMLINK+="rtc_old"KERNEL=="rtc1",SYMLINK+="rtc"
上述规则将原来命名为rtc0的设备链接到rtc old，将rtc1设备链接到rtc。这样，系统会将rtc1设备作为默认的时钟设备。
然后重新加载udev规则，使修改生效
udevadm control --reload-rules重启系统即可。
重启后输入dmesg能看到后面又多出来一段内容，那就是配置系统时间时读取rtc1时间了：
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