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SubjectRe: [PATCH 2/2] watchdog: sama5d4: write the mode register in two steps
On 14/09/2018 12:13:39+0200, Romain Izard wrote:
> The specification for SAMA5D2 and SAMA5D4 chips, that use this IP for
> their watchdog timer, has the following advice regarding the Mode Register:
>
> "When setting the WDDIS bit, and while it is set, the fields WDV and WDD
> must not be modified."
>
> I have observed on a board based on a SAMA5D2 chip that using any other
> timeout duration than the default 16s in the device tree will reset the
> board when the watchdog device is opened; this is probably due to ignoring
> the aforementioned constraint.
>
> To fix this, read the content of the Mode Register before writing it,
> and split the access into two parts if WDV or WDD need to be changed.
>

Hum, that is really weird because when I developed
015b528644a84b0018d3286ecd6ea5f82dce0180, I tested with a program doing:

flags = WDIOS_DISABLECARD;
ioctl(fd, WDIOC_SETOPTIONS, &flags);
for (i = 16; i > 2; i--) {
ioctl(fd, WDIOC_SETTIMEOUT, &i);
}

ioctl(fd, WDIOC_KEEPALIVE, &dummy);

flags = WDIOS_ENABLECARD;
ioctl(fd, WDIOC_SETOPTIONS, &flags);

for (i = 16; i > 2; i--) {
ioctl(fd, WDIOC_SETTIMEOUT, &i);
}

This would immediately reproduce the reset when changing WDV/WDD with
WDDIS set.

I'll test again.

> Signed-off-by: Romain Izard <romain.izard.pro@gmail.com>
> ---
> drivers/watchdog/sama5d4_wdt.c | 27 ++++++++++++++++++++-------
> 1 file changed, 20 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/watchdog/sama5d4_wdt.c b/drivers/watchdog/sama5d4_wdt.c
> index 1e93c1b0e3cf..1e05268ad94b 100644
> --- a/drivers/watchdog/sama5d4_wdt.c
> +++ b/drivers/watchdog/sama5d4_wdt.c
> @@ -46,7 +46,10 @@ MODULE_PARM_DESC(nowayout,
> "Watchdog cannot be stopped once started (default="
> __MODULE_STRING(WATCHDOG_NOWAYOUT) ")");
>
> -#define wdt_enabled (!(wdt->mr & AT91_WDT_WDDIS))
> +#define wdt_enabled(reg) (!((reg) & AT91_WDT_WDDIS))
> +
> +#define wdt_different_counters(reg_a, reg_b) \
> + (((reg_a) ^ (reg_b)) & (AT91_WDT_WDV | AT91_WDT_WDD))
>
> #define wdt_read(wdt, field) \
> readl_relaxed((wdt)->reg_base + (field))
> @@ -78,8 +81,11 @@ static void wdt_write_nosleep(struct sama5d4_wdt *wdt, u32 field, u32 val)
> static int sama5d4_wdt_start(struct watchdog_device *wdd)
> {
> struct sama5d4_wdt *wdt = watchdog_get_drvdata(wdd);
> + u32 reg = wdt_read(wdt, AT91_WDT_MR);
>
> wdt->mr &= ~AT91_WDT_WDDIS;
> + if (!wdt_enabled(reg) && wdt_different_counters(reg, wdt->mr))
> + wdt_write(wdt, AT91_WDT_MR, reg & ~AT91_WDT_WDDIS);
> wdt_write(wdt, AT91_WDT_MR, wdt->mr);
>
> return 0;
> @@ -88,8 +94,11 @@ static int sama5d4_wdt_start(struct watchdog_device *wdd)
> static int sama5d4_wdt_stop(struct watchdog_device *wdd)
> {
> struct sama5d4_wdt *wdt = watchdog_get_drvdata(wdd);
> + u32 reg = wdt_read(wdt, AT91_WDT_MR);
>
> wdt->mr |= AT91_WDT_WDDIS;
> + if (wdt_enabled(reg) && wdt_different_counters(reg, wdt->mr))
> + wdt_write(wdt, AT91_WDT_MR, wdt->mr & ~AT91_WDT_WDDIS);
> wdt_write(wdt, AT91_WDT_MR, wdt->mr);
>
> return 0;
> @@ -122,7 +131,7 @@ static int sama5d4_wdt_set_timeout(struct watchdog_device *wdd,
> * If the watchdog is enabled, then the timeout can be updated. Else,
> * wait that the user enables it.
> */
> - if (wdt_enabled)
> + if (wdt_enabled(wdt->mr))
> wdt_write(wdt, AT91_WDT_MR, wdt->mr & ~AT91_WDT_WDDIS);
>
> wdd->timeout = timeout;
> @@ -186,13 +195,17 @@ static int sama5d4_wdt_init(struct sama5d4_wdt *wdt)
> * If the watchdog is already running, we can safely update it.
> * Else, we have to disable it properly.
> */
> - if (wdt_enabled) {
> + reg = wdt_read(wdt, AT91_WDT_MR);
> + if (wdt_enabled(reg)) {
> + if (!wdt_enabled(wdt->mr))
> + wdt_write_nosleep(wdt, AT91_WDT_MR,
> + wdt->mr & ~AT91_WDT_WDDIS);
> wdt_write_nosleep(wdt, AT91_WDT_MR, wdt->mr);
> - } else {
> - reg = wdt_read(wdt, AT91_WDT_MR);
> - if (!(reg & AT91_WDT_WDDIS))
> + } else if (wdt_enabled(wdt->mr)) {
> + if (wdt_different_counters(reg, wdt->mr))
> wdt_write_nosleep(wdt, AT91_WDT_MR,
> - reg | AT91_WDT_WDDIS);
> + reg & ~AT91_WDT_WDDIS);
> + wdt_write_nosleep(wdt, AT91_WDT_MR, wdt->mr);
> }
> return 0;
> }
> --
> 2.17.1
>

--
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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