[rtc-linux] Re: [PATCH 1/5] rtc: m48t86: verify that the RTC is actually present

Thanks, not tested though, as I am lacking in time at the moment.  I 
probably am the only ts7800 user in the world using a mainline kernel 
too...so will only be punishing myself :-)

Acked-By: Alexander Clouter <redacted>


On 21 February 2017 4:37:35 p.m. Alexandre Belloni 
[off-list ref] wrote:

Hi,

On 15/02/2017 at 09:35:23 -0700, H Hartley Sweeten wrote:

quoted

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.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Alessandro Zummo <redacted>
Cc: Alexandre Belloni <redacted>
Cc: Alexander Clouter <alex@digriz.org.uk>
---
 drivers/rtc/rtc-m48t86.c | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

I've applied that one. Alex, if you are fine with the mach-orion5x
changes, I can take them for 4.11. Else, this will wait for 4.12.

quoted

diff --git a/drivers/rtc/rtc-m48t86.c b/drivers/rtc/rtc-m48t86.c
index 4dc4af4..41ac5d6 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_LEN - 2;
+	unsigned int offset1 = 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))
--

2.10.0

--
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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