diff options
| -rw-r--r-- | drivers/watchdog/imgpdc_wdt.c | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/drivers/watchdog/imgpdc_wdt.c b/drivers/watchdog/imgpdc_wdt.c index 56b8ebcc3775..0f73621827ab 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> |