rtc: tegra: Implement clock handling (5fa40869) · Commits · 戴 / test

Accessing the registers of the RTC block on Tegra requires the module clock to be enabled. This only works because the RTC module clock will be enabled by default during early boot. However, because the clock is unused, the CCF will disable it at late_init time. This causes the RTC to become unusable afterwards. This can easily be reproduced by trying to use the RTC: $ hwclock --rtc /dev/rtc1 This will hang the system. I ran into this by following up on a report by Martin Michlmayr that reboot wasn't working on Tegra210 systems. It turns out that the rtc-tegra driver's ->shutdown() implementation will hang the CPU, because of the disabled clock, before the system can be rebooted. What confused me for a while is that the same driver is used on prior Tegra generations where the hang can not be observed. However, as Peter De Schrijver pointed out, this is because on 32-bit Tegra chips the RTC clock is enabled by the tegra20_timer.c clocksource driver, which uses the RTC to provide a persistent clock. This code is never enabled on 64-bit Tegra because the persistent clock infrastructure does not exist on 64-bit ARM. The proper fix for this is to add proper clock handling to the RTC driver in order to ensure that the clock is enabled when the driver requires it. All device trees contain the clock already, therefore no additional changes are required. Reported-by:

Martin Michlmayr <tbm@cyrius.com> Acked-By Peter De Schrijver <pdeschrijver@nvidia.com> Signed-off-by:

Thierry Reding <treding@nvidia.com> Signed-off-by:

Alexandre Belloni <alexandre.belloni@free-electrons.com>

drivers/rtc/rtc-tegra.c

+26 −2

Original line number	Diff line number	Diff line
		@@ -18,6 +18,7 @@
		* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
		*/

		#include <linux/clk.h>
		#include <linux/delay.h>
		#include <linux/init.h>
		#include <linux/io.h>
		@@ -60,6 +61,7 @@ struct tegra_rtc_info {
		struct platform_device *pdev;
		struct rtc_device *rtc_dev;
		void __iomem rtc_base; / NULL if not initialized. */
		struct clk *clk;
		int tegra_rtc_irq; /* alarm and periodic irq */
		spinlock_t tegra_rtc_lock;
		};
		@@ -327,6 +329,14 @@ static int __init tegra_rtc_probe(struct platform_device *pdev)
		if (info->tegra_rtc_irq <= 0)
		return -EBUSY;

		info->clk = devm_clk_get(&pdev->dev, NULL);
		if (IS_ERR(info->clk))
		return PTR_ERR(info->clk);

		ret = clk_prepare_enable(info->clk);
		if (ret < 0)
		return ret;

		/* set context info. */
		info->pdev = pdev;
		spin_lock_init(&info->tegra_rtc_lock);
		@@ -347,7 +357,7 @@ static int __init tegra_rtc_probe(struct platform_device *pdev)
		ret = PTR_ERR(info->rtc_dev);
		dev_err(&pdev->dev, "Unable to register device (err=%d).\n",
		ret);
		return ret;
		goto disable_clk;
		}

		ret = devm_request_irq(&pdev->dev, info->tegra_rtc_irq,
		@@ -357,11 +367,24 @@ static int __init tegra_rtc_probe(struct platform_device *pdev)
		dev_err(&pdev->dev,
		"Unable to request interrupt for device (err=%d).\n",
		ret);
		return ret;
		goto disable_clk;
		}

		dev_notice(&pdev->dev, "Tegra internal Real Time Clock\n");

		return 0;

		disable_clk:
		clk_disable_unprepare(info->clk);
		return ret;
		}

		static int tegra_rtc_remove(struct platform_device *pdev)
		{
		struct tegra_rtc_info *info = platform_get_drvdata(pdev);

		clk_disable_unprepare(info->clk);

		return 0;
		}

		@@ -414,6 +437,7 @@ static void tegra_rtc_shutdown(struct platform_device *pdev)

		MODULE_ALIAS("platform:tegra_rtc");
		static struct platform_driver tegra_rtc_driver = {
		.remove = tegra_rtc_remove,
		.shutdown = tegra_rtc_shutdown,
		.driver = {
		.name = "tegra_rtc",

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