RE: [PATCH v2] rtc: rtc-at91rm9200: fix uninterruptible wait for ACKUPD

Bryan Evenson
2014-05-07T14:51:43Z

Boris,

> -----Original Message-----
> From: Boris BREZILLON [mailto:boris.brezillon@free-electrons.com]
> Sent: Wednesday, May 07, 2014 6:28 AM
> To: Bryan Evenson
> Cc: Andrew Victor; Nicolas Ferre; Jean-Christophe Plagniol-Villard; linux-arm-
> kernel@lists.infradead.org; Alessandro Zummo; rtc-
> linux@googlegroups.com; linux-kernel@vger.kernel.org; Boris BREZILLON;
> stable@vger.kernel.org
> Subject: [PATCH v2] rtc: rtc-at91rm9200: fix uninterruptible wait for ACKUPD
>
> The rtc user must wait at least 1 sec between each time/calandar update
> (see atmel's datasheet chapter "Updating Time/Calendar").
>
> Use the SECEV interrupt (as suggested by the datasheet) to wait for the RTC
> to be ready for new updates.
>
> Cc: <stable@vger.kernel.org> # v3.10+
> Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
> Reported-by: Bryan Evenson <bevenson@melinkcorp.com>
> ---
> Hello,
>
> This patch fixes a deadlock in an uninterruptible wait when the RTC is
> updated more than once every second.
> AFAICT the bug is here from the beginning, but I think we should at least
> backport this fix to 3.10 and the following longterm and stable releases.
>
> Best Regards,
>
> Boris

Hang on, I found a problem. My system works fine on a soft reboot, but during a power cycle my system hangs. Last thing I see to print is "Uncompressing Linux... done, booting the kernel." If I removde the backup battery for the RTC my system boots just fine. Luckily this is very repeatable on my system. This looks similar to the early rtt-interrupt bug which was fixed about 7 months ago (linux-stable commits 6ce3ee9af1ad697c71766067ffa1a35352dfdcfd and 54f830b7337ed016b6708cf5a2ac297d4cee227d). I confirmed that the kernel I'm using has the relevant fix applied from 7 months ago. Did this fix reintroduce the early rtt-interrupt bug?

Let me know if you would like me to test anything or more information.

Regards,
Bryan

>
> Changes since v1:
> - disable SECEV interrupt when the RTC is ready to accept new time updates
>
> drivers/rtc/rtc-at91rm9200.c | 16 ++++++++++++++--
> 1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/rtc/rtc-at91rm9200.c b/drivers/rtc/rtc-at91rm9200.c index
> 3281c90..44fe83e 100644
> --- a/drivers/rtc/rtc-at91rm9200.c
> +++ b/drivers/rtc/rtc-at91rm9200.c
> @@ -48,6 +48,7 @@ struct at91_rtc_config {
>
> static const struct at91_rtc_config *at91_rtc_config; static
> DECLARE_COMPLETION(at91_rtc_updated);
> +static DECLARE_COMPLETION(at91_rtc_upd_rdy);
> static unsigned int at91_alarm_year = AT91_RTC_EPOCH; static void
> __iomem *at91_rtc_regs; static int irq; @@ -161,6 +162,8 @@ static int
> at91_rtc_settime(struct device *dev, struct rtc_time *tm)
> 1900 + tm->tm_year, tm->tm_mon, tm->tm_mday,
> tm->tm_hour, tm->tm_min, tm->tm_sec);
>
> + wait_for_completion(&at91_rtc_upd_rdy);
> +
> /* Stop Time/Calendar from counting */
> cr = at91_rtc_read(AT91_RTC_CR);
> at91_rtc_write(AT91_RTC_CR, cr | AT91_RTC_UPDCAL |
> AT91_RTC_UPDTIM); @@ -183,7 +186,9 @@ static int
> at91_rtc_settime(struct device *dev, struct rtc_time *tm)
>
> /* Restart Time/Calendar */
> cr = at91_rtc_read(AT91_RTC_CR);
> + at91_rtc_write(AT91_RTC_SCCR, AT91_RTC_SECEV);
> at91_rtc_write(AT91_RTC_CR, cr & ~(AT91_RTC_UPDCAL |
> AT91_RTC_UPDTIM));
> + at91_rtc_write_ier(AT91_RTC_SECEV);
>
> return 0;
> }
> @@ -290,8 +295,10 @@ static irqreturn_t at91_rtc_interrupt(int irq, void
> *dev_id)
> if (rtsr) { /* this interrupt is shared! Is it ours? */
> if (rtsr & AT91_RTC_ALARM)
> events |= (RTC_AF | RTC_IRQF);
> - if (rtsr & AT91_RTC_SECEV)
> - events |= (RTC_UF | RTC_IRQF);
> + if (rtsr & AT91_RTC_SECEV) {
> + complete(&at91_rtc_upd_rdy);
> + at91_rtc_write_idr(AT91_RTC_SECEV);
> + }
> if (rtsr & AT91_RTC_ACKUPD)
> complete(&at91_rtc_updated);
>
> @@ -413,6 +420,11 @@ static int __init at91_rtc_probe(struct
> platform_device *pdev)
> return PTR_ERR(rtc);
> platform_set_drvdata(pdev, rtc);
>
> + /* enable SECEV interrupt in order to initialize at91_rtc_upd_rdy
> + * completion.
> + */
> + at91_rtc_write_ier(AT91_RTC_SECEV);
> +
> dev_info(&pdev->dev, "AT91 Real Time Clock driver.\n");
> return 0;
> }
> --
> 1.8.3.2