On Thu, Jun 15, 2017 at 06:06:04PM +0800, Peter Chen wrote: > On Thu, Jun 15, 2017 at 11:35:20AM +0200, Ulf Hansson wrote: > > On 15 June 2017 at 11:11, Peter Chen <hzpeterchen@xxxxxxxxx> wrote: > > > On Thu, Jun 15, 2017 at 10:11:45AM +0200, Ulf Hansson wrote: > > >> > Yes, you are right. This is the limitation for this power sequence > > >> > library, the registration for the 1st power sequence instance must > > >> > be finished before device driver uses it. I am appreciated that > > >> > you can supply some suggestions for it. > > >> > > >> In general this kind of problems is solved by first parsing the DTB, > > >> which means you will find out whether there is a resource (a pwrseq) > > >> required for the device. Then you try to fetch that resource, and if > > >> that fails, it means the resource is not yet available, and hence you > > >> want to retry later and should return -EPROBE_DEFER. > > >> > > >> In this case, of_pwrseq_on() needs to be converted to start looking > > >> for a pwrseq compatible in it's child node - I guess. Then if that is > > >> found, you try to fetch the instance of the corresponding library. > > >> Failing to fetch the library instance should then cause a return > > >> -EPROBE_DEFER. > > > > > > The most difficulty for this is we can't know whether the requested > > > pwrseq instance will be registered or not, the kernel configuration > > > for this pwrseq library may not be chosen at all. > > > > In such case it is still correct to return -EPROBE_DEFER, because the > > driver that tries to probe its device will fail unless it can run the > > needed pwrseq. Right? > > > > Unlike the MMC design, there is no dts entry to indicate whether this > device needs pwrseq or not at this design, it will only carry out power > on sequence after matching. So, return -EPROBE_DEFER may not work since > this device may never need pwrseq. > Ulf, since it is the use case limitation, it can't work like device driver. Do you have more comments for it, thanks. Peter > > > > > >> > > >> > > > >> >> Moreover, I have found yet another severe problem but reviewing the code: > > >> >> In the struct pwrseq, you have a "bool used", which you are setting to > > >> >> "true" once the pwrseq has been hooked up with the device, when a > > >> >> driver calls of_pwrseq_on(). Setting that variable to true, will also > > >> >> prevent another driver from using the same instance of the pwrseq for > > >> >> its device. So, to cope with multiple users, you register a new > > >> >> instance of the same pwrseq library that got hooked up, once the > > >> >> ->get() callback is about to complete. > > >> >> > > >> >> The problem the occurs, when there is another driver calling > > >> >> of_pwrseq_on() in between, meaning that the new instance has not yet > > >> >> been registered. This will simply fail, won't it? > > >> > > > >> > Yes, you are right, thanks for pointing that, I will add mutex_lock for > > >> > of_pwrseq_on. > > >> > > >> Another option is to entirely skip to two step approach. > > >> > > >> In other words, make the library to cope with multiple users via the > > >> same registered library instance. > > >> > > > > > > No, the pwrseq instance stores dtb information (clock, gpio, etc), it > > > needs to be per device. > > > > I think you misunderstood my suggestion here. Of course you need to > > allocate one pwrseq data per device. > > > > However, my point is that you shouldn't need more than one instance of > > the library functions to be registered in the list of available pwrseq > > libraries. > > > > This additional instance is used to store compatible information for > this pwrseq library, it is used for the next matching between device > and pwrseq library, it just likes we need the first pwrseq instance > registered at boot stage. > > -- > > Best Regards, > Peter Chen > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel -- Best Regards, Peter Chen -- 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
