Hi Guenter, On 10 June 2015 at 11:41, Fu Wei <fu.wei@xxxxxxxxxx> wrote: > Hi Guenter, > > On 10 June 2015 at 00:45, Guenter Roeck <linux@xxxxxxxxxxxx> wrote: >> On 06/09/2015 09:29 AM, Timur Tabi wrote: >>> >>> On 06/09/2015 11:22 AM, Guenter Roeck wrote: >>>> >>>> >>>> >>>> but I see your point. Essentially, the specification is broken >>>> for all practical purposes, since, as you point out, enabling >>>> the watchdog overwrites and explicitly sets WCV. Effectively >>>> this means that just using WCV to program the timeout period >>>> is not really possible. >>>> >>>> I am not really sure how to address this. We can either only use WOR, >>>> and forget about pretimeout, or we can enforce a minimum pretimeout. >>>> In the latter case, we'll have to write WCV after writing WOR. >>> >>> >>> In talking with our hardware engineers, using WCV to program the timeout >>> period is not a valid operation. This is why I keep arguing against the >>> pre-timeout feature, and I don't agree that servers should always use >>> pre-timeout. >>> >> >> Not sure if "not valid" is correct - after all, it is mentioned in the >> specification. However, it is at the very least fragile. > > I think we should focus on SBSA spec, but not a specific chip design, > because this is SBSA watchdog, not a driver for an IP core from a > specific chip vendor. > this operation is mentioned in the spec, > and I have tested my driver on Foundation model(from ARM) and a real hardware. > >> >> I tend to agree that we should just forget about pretimeout and >> use your original approach, where the timeout value is used >> to program WOR. Everything else is really just asking for trouble. Another weakness of only using WOR is the timeout limited by this 32bit register. 10s @400MHz generic Timer I don't think this limit is good for a server, once the server is in a heavy load > > I don't mind if we give up pretimeout, The reason I use pretimeout is: > this concept matches the function of two stage timeouts. > > but, If we give up pretimeout, could you give me a suggestion: > > How to config the two stage timeouts > (1)from enabling watchdog to WS0 > (2)the time from WS1 to WS0 > > If we only have one timeout parameter, How to config the two stage timeouts? > Any suggestion ? > > If we make the first stage timeout is timeout/2, this violates the > definition of timeout. > I don't think users expect interrupt, panic or reboot at timeout/2. > > And WS1 definitely isn't a backup of WS0. > >> >> Guenter >> > > > > -- > Best regards, > > Fu Wei > Software Engineer > Red Hat Software (Beijing) Co.,Ltd.Shanghai Branch > Ph: +86 21 61221326(direct) > Ph: +86 186 2020 4684 (mobile) > Room 1512, Regus One Corporate Avenue,Level 15, > One Corporate Avenue,222 Hubin Road,Huangpu District, > Shanghai,China 200021 -- Best regards, Fu Wei Software Engineer Red Hat Software (Beijing) Co.,Ltd.Shanghai Branch Ph: +86 21 61221326(direct) Ph: +86 186 2020 4684 (mobile) Room 1512, Regus One Corporate Avenue,Level 15, One Corporate Avenue,222 Hubin Road,Huangpu District, Shanghai,China 200021 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
