The m48t86 has 114 bytes of user space available, so we can use this space to detect for the presence of the RTC.
Signed-off-by: Alexander Clouter <[email protected]> --- drivers/rtc/rtc-m48t86.c | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) diff --git a/drivers/rtc/rtc-m48t86.c b/drivers/rtc/rtc-m48t86.c index 6f99e64..b8edf73 100644 --- a/drivers/rtc/rtc-m48t86.c +++ b/drivers/rtc/rtc-m48t86.c @@ -173,6 +173,41 @@ static const struct rtc_class_ops m48t86_rtc_ops = { .proc = m48t86_rtc_proc, }; +/* + * The RTC chip has 114 bytes upper bytes that can be used as user storage + * space which we can use to test if the chip is present; for example it is + * an optional feature and not all boards will have it present. + * + * I've used the method Technologic Systems use in their rtc7800.c example + * for the detection. + * + * TODO: track down a guinea pig without an RTC to see if we can work out a + * better RTC detection routine + */ +static int m48t86_rtc_detect(struct device *dev) +{ + unsigned char tmp_rtc0, tmp_rtc1; + + tmp_rtc0 = m48t86_rtc_readbyte(dev, 126); + tmp_rtc1 = m48t86_rtc_readbyte(dev, 127); + + m48t86_rtc_writebyte(dev, 0x00, 126); + m48t86_rtc_writebyte(dev, 0x55, 127); + if (m48t86_rtc_readbyte(dev, 127) == 0x55) { + m48t86_rtc_writebyte(dev, 0xaa, 127); + if (m48t86_rtc_readbyte(dev, 127) == 0xaa + && m48t86_rtc_readbyte(dev, 126) == 0x00) { + m48t86_rtc_writebyte(dev, tmp_rtc0, 126); + m48t86_rtc_writebyte(dev, tmp_rtc1, 127); + + return 0; + } + } + + dev_info(dev, "RTC not found\n"); + return -ENODEV; +} + static int m48t86_rtc_probe(struct platform_device *pdev) { unsigned char reg; @@ -232,6 +267,14 @@ static int m48t86_rtc_probe(struct platform_device *pdev) } else priv->ops = pdev->dev.platform_data; + err = m48t86_rtc_detect(&pdev->dev); + if (err) { + if (!pdev->dev.platform_data) + goto out_io_data; + else + goto out_free; + } + priv->rtc = rtc_device_register("m48t86", &pdev->dev, &m48t86_rtc_ops, THIS_MODULE); if (IS_ERR(priv->rtc)) { -- 1.7.10.4 _______________________________________________ devicetree-discuss mailing list [email protected] https://lists.ozlabs.org/listinfo/devicetree-discuss
