[PATCH 2/4] watchdog: sama5d4: fix race condition

From: Alexandre Belloni
Date: Fri Mar 03 2017 - 03:20:05 EST


WDT_MR and WDT_CR must not updated within three slow clock periods after
the last ping (write to WDT_CR or WDT_MR). Ensure enough time has elapsed
before writing those registers.
wdt_write() waits for 4 periods to ensure at least 3 edges are seen by the
IP.

Signed-off-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxxxxxxxxx>
---
drivers/watchdog/sama5d4_wdt.c | 33 +++++++++++++++++++++++++++++----
1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/drivers/watchdog/sama5d4_wdt.c b/drivers/watchdog/sama5d4_wdt.c
index 5cee20caca78..362fd229786d 100644
--- a/drivers/watchdog/sama5d4_wdt.c
+++ b/drivers/watchdog/sama5d4_wdt.c
@@ -6,6 +6,7 @@
* Licensed under GPLv2.
*/

+#include <linux/delay.h>
#include <linux/interrupt.h>
#include <linux/io.h>
#include <linux/kernel.h>
@@ -29,6 +30,7 @@ struct sama5d4_wdt {
struct watchdog_device wdd;
void __iomem *reg_base;
u32 mr;
+ unsigned long last_ping;
};

static int wdt_timeout = WDT_DEFAULT_TIMEOUT;
@@ -49,8 +51,29 @@ MODULE_PARM_DESC(nowayout,
#define wdt_read(wdt, field) \
readl_relaxed((wdt)->reg_base + (field))

-#define wdt_write(wtd, field, val) \
- writel_relaxed((val), (wdt)->reg_base + (field))
+/* 4 slow clock periods is 4/32768 = 122.07Âs*/
+#define WDT_DELAY usecs_to_jiffies(123)
+
+static void wdt_write(struct sama5d4_wdt *wdt, u32 field, u32 val)
+{
+ /*
+ * WDT_CR and WDT_MR must not be modified within three slow clock
+ * periods following a restart of the watchdog performed by a write
+ * access in WDT_CR.
+ */
+ while (time_before(jiffies, wdt->last_ping + WDT_DELAY))
+ usleep_range(30, 125);
+ writel_relaxed(val, wdt->reg_base + field);
+ wdt->last_ping = jiffies;
+}
+
+static void wdt_write_nosleep(struct sama5d4_wdt *wdt, u32 field, u32 val)
+{
+ if (time_before(jiffies, wdt->last_ping + WDT_DELAY))
+ udelay(123);
+ writel_relaxed(val, wdt->reg_base + field);
+ wdt->last_ping = jiffies;
+}

static int sama5d4_wdt_start(struct watchdog_device *wdd)
{
@@ -164,11 +187,12 @@ static int sama5d4_wdt_init(struct sama5d4_wdt *wdt)
* Else, we have to disable it properly.
*/
if (wdt_enabled) {
- wdt_write(wdt, AT91_WDT_MR, wdt->mr);
+ wdt_write_nosleep(wdt, AT91_WDT_MR, wdt->mr);
} else {
reg = wdt_read(wdt, AT91_WDT_MR);
if (!(reg & AT91_WDT_WDDIS))
- wdt_write(wdt, AT91_WDT_MR, reg | AT91_WDT_WDDIS);
+ wdt_write_nosleep(wdt, AT91_WDT_MR,
+ reg | AT91_WDT_WDDIS);
}
return 0;
}
@@ -193,6 +217,7 @@ static int sama5d4_wdt_probe(struct platform_device *pdev)
wdd->ops = &sama5d4_wdt_ops;
wdd->min_timeout = MIN_WDT_TIMEOUT;
wdd->max_timeout = MAX_WDT_TIMEOUT;
+ wdt->last_ping = jiffies;

watchdog_set_drvdata(wdd, wdt);

--
2.11.0