[PATCH v15 2/7] power: add power sequence library

[hzpeterchen@gmail.com (Peter Chen)]

On Wed, Jun 14, 2017 at 10:53:29AM +0200, Ulf Hansson wrote:
> On 14 June 2017 at 03:53, Peter Chen <hzpeterchen@gmail.com> wrote:
> > On Tue, Jun 13, 2017 at 12:24:42PM +0200, Ulf Hansson wrote:
> >> [...]
> >>
> >> > +
> >> > +/**
> >> > + * of_pwrseq_on - Carry out power sequence on for device node
> >> > + *
> >> > + * @np: the device node would like to power on
> >> > + *
> >> > + * Carry out a single device power on.  If multiple devices
> >> > + * need to be handled, use of_pwrseq_on_list() instead.
> >> > + *
> >> > + * Return a pointer to the power sequence instance on success,
> >> > + * or an error code otherwise.
> >> > + */
> >> > +struct pwrseq *of_pwrseq_on(struct device_node *np)
> >> > +{
> >> > +       struct pwrseq *pwrseq;
> >> > +       int ret;
> >> > +
> >> > +       pwrseq = pwrseq_find_available_instance(np);
> >> > +       if (!pwrseq)
> >> > +               return ERR_PTR(-ENOENT);
> >>
> >> In case the pwrseq instance hasn't been registered yet, then there is
> >> no way to deal with -EPROBE_DEFER properly here.
> >>
> >> I haven't been following the discussions in-depth during all
> >> iterations, so perhaps you have already discussed why doing it like
> >> this.
> >
> > Yes, it has been discussed. In order to compare with compatible string
> > at dts, we need to have one registered pwrseq instance for each
> > pwrseq library, this pre-registered one is allocated using
> > postcore_initcall, and the new (eg, second) instance is registered
> > after pwrseq_get has succeeded.
> 
> I understand you need one compatible per pwrseq library, but how does
> that have anything to do with -EPROBE_DEFER?
> 
> My point is that, if a driver calls of_pwrseq_on() (which calls
> pwrseq_find_available_instance()), but the corresponding pwrseq
> library and instance has not yet been registered for that device. Then
> how will you handle -EPROBE_DEFER? I guess you simply can't, which is
> why *all* pwrseq libraries needs to be registered in early boot phase,
> like at postcore_initcall(). Right?
> 
> If that is the case, I really don't like it.
> 

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.

> 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.

> 
> Sorry for jumping in late, however to me it seems like there is still
> some pieces missing to make this work.
> 
> [...]
> 
> Kind regards
> Uffe

-- 

Best Regards,
Peter Chen