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| author | Ezequiel Garcia <ezequiel.garcia@imgtec.com> | 2015-05-11 20:41:05 +0300 |
|---|---|---|
| committer | Wim Van Sebroeck <wim@iguana.be> | 2015-06-22 16:54:15 +0300 |
| commit | c1f263878e99e44c6e23fee0dfe01ef05ad83024 (patch) | |
| tree | 889bdb164bc69be54df39ff51d1cfd5c146dcdbe | |
| parent | deb8d50eb40085d304b42a524d4ba326fcecc73d (diff) | |
| download | linux-c1f263878e99e44c6e23fee0dfe01ef05ad83024.tar.xz | |
watchdog: imgpdc: Add some documentation about the timeout
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@imgtec.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
| -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> |