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

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Message-ID: <20161115154124.GI4082@atomide.com>
Date:   Tue, 15 Nov 2016 07:41:24 -0800
From:   Tony Lindgren <tony@...mide.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Haojian Zhuang <haojian.zhuang@...aro.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Nishanth Menon <nm@...com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux-OMAP <linux-omap@...r.kernel.org>
Subject: Re: [PATCH 1/5] pinctrl: core: Use delayed work for hogs

* Linus Walleij <linus.walleij@...aro.org> [161114 22:53]:
> On Tue, Nov 15, 2016 at 1:47 AM, Tony Lindgren <tony@...mide.com> wrote:
> 
> > 8< --------------------------------
> > From tony Mon Sep 17 00:00:00 2001
> > From: Tony Lindgren <tony@...mide.com>
> > Date: Tue, 25 Oct 2016 08:33:35 -0700
> > Subject: [PATCH] pinctrl: core: Use delayed work for hogs
> >
> > Having the pin control framework call pin controller functions
> > before it's probe has finished is not nice as the pin controller
> > device driver does not yet have struct pinctrl_dev handle.
> >
> > Let's fix this issue by adding deferred work for late init. This is
> > needed to be able to add pinctrl generic helper functions that expect
> > to know struct pinctrl_dev handle. Note that we now need to call
> > create_pinctrl() directly as we don't want to add the pin controller
> > to the list of controllers until the hogs are claimed. We also need
> > to pass the pinctrl_dev to the device tree parser functions as they
> > otherwise won't find the right controller at this point.
> >
> > Signed-off-by: Tony Lindgren <tony@...mide.com>
> 
> This looks a lot better!
> 
> So if I understand correctly, we can guarantee that the delayed
> work will not execute until the device driver probe() has finished,
> and it *will* execute immediately after that?
> 
> So:
> - Device driver probes
> - Delayed work is called
> - Next initcall
> 
> I'm not 100% familiar with how delayed work works... :/

Yeah well the delayed work gets scheduled for next jiffy but may
be pre-empted as it runs in process context.

So in the worst case it could that we still may need to fix few
drivers to support -EPROBE_DEFER. I wonder if we should check for
hogs in probe already and only defer if hogs are defined?

Regards,

Tony