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

Boris BREZILLON
2014-05-07T10:28:21Z

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

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