rtc: m48t86: verify that the RTC is actually present (3ea07127) · Commits · 戴 / test

drivers/rtc/rtc-m48t86.c

+36 −0

Original line number	Diff line number	Diff line
		@@ -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))

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