This watchdog hardware can be configured in terms of power-of-two clock cycles. Therefore, the watchdog timeout configured by the user will be rounded-up to the next possible hardware timeout. This commit adds a comment explaining this. Signed-off-by: Ezequiel Garcia <ezequiel.garcia@xxxxxxxxxx> --- drivers/watchdog/imgpdc_wdt.c | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/drivers/watchdog/imgpdc_wdt.c b/drivers/watchdog/imgpdc_wdt.c index 56b8ebc..0f73621 100644 --- a/drivers/watchdog/imgpdc_wdt.c +++ b/drivers/watchdog/imgpdc_wdt.c @@ -9,6 +9,35 @@ * * Based on drivers/watchdog/sunxi_wdt.c Copyright (c) 2013 Carlo Caione * 2012 Henrik Nordstrom + * + * Notes + * ----- + * The timeout value is rounded to the next power of two clock cycles. + * This is configured using the PDC_WDT_CONFIG register, according to this + * formula: + * + * timeout = 2^(delay + 1) clock cycles + * + * Where 'delay' is the value written in PDC_WDT_CONFIG register. + * + * Therefore, the hardware only allows to program watchdog timeouts, expressed + * as a power of two number of watchdog clock cycles. The current implementation + * guarantees that the actual watchdog timeout will be _at least_ the value + * programmed in the imgpdg_wdt driver. + * + * The following table shows how the user-configured timeout relates + * to the actual hardware timeout (watchdog clock @ 40000 Hz): + * + * input timeout | WD_DELAY | actual timeout + * ----------------------------------- + * 10 | 18 | 13 seconds + * 20 | 19 | 26 seconds + * 30 | 20 | 52 seconds + * 60 | 21 | 104 seconds + * + * Albeit coarse, this granularity would suffice most watchdog uses. + * If the platform allows it, the user should be able to change the watchdog + * clock rate and achieve a finer timeout granularity. */ #include <linux/clk.h> -- 2.3.3 -- To unsubscribe from this list: send the line "unsubscribe linux-watchdog" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
