This is a note to let you know that I've just added the patch titled rtc: tegra: Implement clock handling to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: rtc-tegra-implement-clock-handling.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 5fa4086987506b2ab8c92f8f99f2295db9918856 Mon Sep 17 00:00:00 2001 From: Thierry Reding <treding@xxxxxxxxxx> Date: Thu, 12 Jan 2017 17:07:43 +0100 Subject: rtc: tegra: Implement clock handling From: Thierry Reding <treding@xxxxxxxxxx> commit 5fa4086987506b2ab8c92f8f99f2295db9918856 upstream. 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@xxxxxxxxxx> Acked-By Peter De Schrijver <pdeschrijver@xxxxxxxxxx> Signed-off-by: Thierry Reding <treding@xxxxxxxxxx> Signed-off-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxxxxxxxxx> [bwh: Backported to 4.9: adjust context] Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/rtc/rtc-tegra.c | 28 ++++++++++++++++++++++++++-- 1 file changed, 26 insertions(+), 2 deletions(-) --- a/drivers/rtc/rtc-tegra.c +++ b/drivers/rtc/rtc-tegra.c @@ -18,6 +18,7 @@ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ #include <linux/kernel.h> +#include <linux/clk.h> #include <linux/init.h> #include <linux/module.h> #include <linux/slab.h> @@ -59,6 +60,7 @@ 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; }; @@ -326,6 +328,14 @@ static int __init tegra_rtc_probe(struct 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); @@ -346,7 +356,7 @@ static int __init tegra_rtc_probe(struct 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, @@ -356,12 +366,25 @@ static int __init tegra_rtc_probe(struct 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; } #ifdef CONFIG_PM_SLEEP @@ -413,6 +436,7 @@ static void tegra_rtc_shutdown(struct pl MODULE_ALIAS("platform:tegra_rtc"); static struct platform_driver tegra_rtc_driver = { + .remove = tegra_rtc_remove, .shutdown = tegra_rtc_shutdown, .driver = { .name = "tegra_rtc", Patches currently in stable-queue which might be from treding@xxxxxxxxxx are queue-4.9/rtc-tegra-implement-clock-handling.patch