diff options
Diffstat (limited to 'drivers/rtc')
| -rw-r--r-- | drivers/rtc/rtc-m48t86.c | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/drivers/rtc/rtc-m48t86.c b/drivers/rtc/rtc-m48t86.c index 4dc4af41c03d..491e8e4b300b 100644 --- a/drivers/rtc/rtc-m48t86.c +++ b/drivers/rtc/rtc-m48t86.c @@ -201,6 +201,37 @@ static ssize_t m48t86_nvram_write(struct file *filp, struct kobject *kobj, static BIN_ATTR(nvram, 0644, m48t86_nvram_read, m48t86_nvram_write, M48T86_NVRAM_LEN); +/* + * The RTC is an optional feature at purchase time on some Technologic Systems + * boards. Verify that it actually exists by checking if the last two bytes + * of the NVRAM can be changed. + * + * This is based on the method used in their rtc7800.c example. + */ +static bool m48t86_verify_chip(struct platform_device *pdev) +{ + unsigned int offset0 = M48T86_NVRAM(M48T86_NVRAM_LEN - 2); + unsigned int offset1 = M48T86_NVRAM(M48T86_NVRAM_LEN - 1); + unsigned char tmp0, tmp1; + + tmp0 = m48t86_readb(&pdev->dev, offset0); + tmp1 = m48t86_readb(&pdev->dev, offset1); + + m48t86_writeb(&pdev->dev, 0x00, offset0); + m48t86_writeb(&pdev->dev, 0x55, offset1); + if (m48t86_readb(&pdev->dev, offset1) == 0x55) { + m48t86_writeb(&pdev->dev, 0xaa, offset1); + if (m48t86_readb(&pdev->dev, offset1) == 0xaa && + m48t86_readb(&pdev->dev, offset0) == 0x00) { + m48t86_writeb(&pdev->dev, tmp0, offset0); + m48t86_writeb(&pdev->dev, tmp1, offset1); + + return true; + } + } + return false; +} + static int m48t86_rtc_probe(struct platform_device *pdev) { struct m48t86_rtc_info *info; @@ -231,6 +262,11 @@ static int m48t86_rtc_probe(struct platform_device *pdev) dev_set_drvdata(&pdev->dev, info); + if (!m48t86_verify_chip(pdev)) { + dev_info(&pdev->dev, "RTC not present\n"); + return -ENODEV; + } + info->rtc = devm_rtc_device_register(&pdev->dev, "m48t86", &m48t86_rtc_ops, THIS_MODULE); if (IS_ERR(info->rtc)) |