Dear Guenter, On Mon, 26 Jan 2015 20:08:04 -0800 Guenter Roeck <linux@xxxxxxxxxxxx> wrote: > On 01/26/2015 07:49 PM, Jisheng Zhang wrote: > > Dear Doug, > > > > On Mon, 26 Jan 2015 15:27:15 -0800 > > Doug Anderson <dianders@xxxxxxxxxxxx> wrote: > > > >> On some dw_wdt implementations the "top" register may be initted to 0 > >> at bootup. In such a case, each "pat" of the watchdog will reset the > >> timer to 0xffff. That's pretty short. > >> > >> The input clock of the wdt can be any of a wide range of values. On > >> an rk3288 system, I've seen the wdt clock be 24.75 MHz. That means > >> each tick is ~40ns and we'll count to 0xffff in ~2.6ms. > >> > >> Because of the above two facts, it's a really good idea to pat the > >> watchdog after initting the "top" register properly and before > >> enabling the watchdog. If you don't then there's no way we'll get the > >> next heartbeat in time. > >> > >> Jisheng Zhang fixed this problem on some dw_mmc versions by using the > > > > s/dw_mmc/dw_wdt > > > >> TOP_INIT feature. However, the dw_wdt on rk3288 doesn't have TOP_INIT > >> so it's a good idea to also pat the watchdog manually. > > > > Based on your register dumping, I see the following configurations on > > rk3288: > > > > WDT_DUAL_TOP is configured as false, so there's no TOP_INIT > > > > WDT_DFLT_TOP is configured as 0, so it will timeout soon. > > > > > > So an extra pat is a must on such platforms with similar configurations. > > And it doesn't hurt anything if we have an extra pat before enabling the > > WDT > > > > All in all, except the "dw_mmc" typo above, the patch looks good to me. > > > > Jisheng, > > it would be great if you can provide configuration information shown in > the (undocumented) registers. The wdt in rk3288 is a bit old, so I'm not sure whether the meaning is the same or not. The key related configuration here is the so called CP_WDT_DUAL_TOP, bit[2] of WDT_COMP_PARAMS_1 (0xf4), which indicates whether the TOP_INIT bits exist or fixed as zero. Thanks, Jisheng > > Doug, > > can you send another version with this information added as comment > to the code ? This will help others to understand what is going on > (and why) later on. > > Thanks, > Guenter > -- 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
