Re: [PATCH 1/5] pinctrl: core: Use delayed work for hogs

[Tony Lindgren]

* Tony Lindgren <tony@xxxxxxxxxxx> [161111 12:27]:
> * Linus Walleij <linus.walleij@xxxxxxxxxx> [161111 12:17]:
> > On Tue, Oct 25, 2016 at 11:02 PM, Tony Lindgren <tony@xxxxxxxxxxx> wrote:
> > > Signed-off-by: Tony Lindgren <tony@xxxxxxxxxxx>
> > 
> > I don't see why this is necessary?
> 
> It's needed because the pin controller driver has not yet
> finished it's probe at this point. We end up calling functions
> in the device driver where no struct pinctrl_dev is yet known
> to the driver. Asking a device driver to do something before
> it's probe is done does not quite follow the Linux driver model :)
> 
> > The hogging was placed inside pinctrl_register() so that any hogs
> > would be taken before it returns, so nothing else can take it
> > before the controller itself has the first chance. This semantic
> > needs to be preserved I think.
> > 
> > > +       schedule_delayed_work(&pctldev->hog_work,
> > > +                                     msecs_to_jiffies(100));
> > 
> > If we arbitrarily delay, something else can go in and take the
> > pins used by the hogs before the pinctrl core? That is what
> > we want to avoid.
> > 
> > Hm, 100ms seems arbitrarily chosen BTW. Can it be 1 ms?
> > 1 ns?
> 
> Yeah well seems like it should not matter but the race we need
> to remove somehow.
> 
> > I'm pretty sure that whatever it is that needs to happen before
> > the hog work runs can race with this delayed work under
> > some circumstances (such as slow external expanders
> > on i2c). It should be impossible for that to happen
> > and I don't think it is?
> 
> Yes it's totally possible even with delay set to 0.
> 
> Maybe we could add some trigger on the first consumer request
> and if that does not happen use the timer?

Below is what I came up with for removing the race for hogs. We
can do it by not registering the pctldev until in the deferred
work, does that seem OK to you?

Regards,

Tony

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