On Thu, Jan 12, 2017 at 05:07:43PM +0100, Thierry Reding wrote:
> From: Thierry Reding <treding@xxxxxxxxxx>
>
> 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
> of 64-bit ARM.
'on 64-bit ARM' I guess?
Other than that Acked-By Peter De Schrijver <pdeschrijver@xxxxxxxxxx>
>
> 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.
>
> Cc: Peter De Schrijver <pdeschrijver@xxxxxxxxxx>
> Reported-by: Martin Michlmayr <tbm@xxxxxxxxxx>
> Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
> ---
> drivers/rtc/rtc-tegra.c | 28 ++++++++++++++++++++++++++--
> 1 file changed, 26 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/rtc/rtc-tegra.c b/drivers/rtc/rtc-tegra.c
> index 38e662ff1a70..d30d57b048d3 100644
> --- 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/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,
> @@ -357,12 +367,25 @@ 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;
> }
>
> #ifdef CONFIG_PM_SLEEP
> @@ -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",
> --
> 2.11.0
>
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