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

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Message-ID: <20170110153045.GS2630@atomide.com>
Date:   Tue, 10 Jan 2017 07:30:46 -0800
From:   Tony Lindgren <tony@...mide.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        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@...r.kernel.org" <linux-omap@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH 1/5] pinctrl: core: Use delayed work for hogs

* Geert Uytterhoeven <geert@...ux-m68k.org> [170110 06:09]:
> Hi Tony,
> 
> On Tue, Dec 27, 2016 at 6:19 PM, Tony Lindgren <tony@...mide.com> wrote:
> > 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>
> 
> I believe this patch causes a regression on r8a7740/armadillo, where the
> pin controller is also a GPIO controller, and lcd0 needs a hog
> (cfr. arch/arm/boot/dts/r8a7740-armadillo800eva.dts):
> 
> -GPIO line 176 (lcd0) hogged as output/high
> -sh-pfc e6050000.pfc: r8a7740_pfc handling gpio 0 -> 211
> +gpiochip_add_data: GPIOs 0..211 (r8a7740_pfc) failed to register
> +sh-pfc e6050000.pfc: failed to init GPIO chip, ignoring...
>  sh-pfc e6050000.pfc: r8a7740_pfc support registered
> 
> Hence all drivers using GPIOs fail to initialize because their GPIOs never
> become available.
> 
> Adding debug prints to the failure paths shows that the call to
> of_pinctrl_get() in of_gpiochip_add_pin_range() fails with -EPROBE_DEFER.
> Adding a debug print to the top of gpiochip_add_data() makes the problem go
> away, presumably because it introduces a delay that allows the delayed work
> to kick in...

OK. What if we added also an optional pinctrl function that the pin
controller driver could call to initialize hogs? Then the pin controller
driver could call it during or after probe as needed. That is after
there's a valid struct pinctrl_dev handle.

> Jon's fix ("pinctrl: core: Fix panic when pinctrl devices with hogs are
> unregistered") doesn't help, as it affects unregistration only.
> 
> > --- a/drivers/pinctrl/core.c
> > +++ b/drivers/pinctrl/core.c
> 
> > @@ -1800,32 +1847,10 @@ struct pinctrl_dev *pinctrl_register(struct pinctrl_desc *pctldesc,
> >                 goto out_err;
> >         }
> >
> > -       mutex_lock(&pinctrldev_list_mutex);
> > -       list_add_tail(&pctldev->node, &pinctrldev_list);
> > -       mutex_unlock(&pinctrldev_list_mutex);
> > -
> > -       pctldev->p = pinctrl_get(pctldev->dev);
> > -
> > -       if (!IS_ERR(pctldev->p)) {
> > -               pctldev->hog_default =
> > -                       pinctrl_lookup_state(pctldev->p, PINCTRL_STATE_DEFAULT);
> > -               if (IS_ERR(pctldev->hog_default)) {
> > -                       dev_dbg(dev, "failed to lookup the default state\n");
> > -               } else {
> > -                       if (pinctrl_select_state(pctldev->p,
> > -                                               pctldev->hog_default))
> > -                               dev_err(dev,
> > -                                       "failed to select default state\n");
> > -               }
> > -
> > -               pctldev->hog_sleep =
> > -                       pinctrl_lookup_state(pctldev->p,
> > -                                                   PINCTRL_STATE_SLEEP);
> > -               if (IS_ERR(pctldev->hog_sleep))
> > -                       dev_dbg(dev, "failed to lookup the sleep state\n");
> > -       }
> > -
> > -       pinctrl_init_device_debugfs(pctldev);
> > +       if (pinctrl_dt_has_hogs(pctldev))
> 
> Changing the above line to "if (0 && pinctrl_dt_has_hogs(pctldev))"
> fixes the issue for me.
> 
> > +               schedule_delayed_work(&pctldev->late_init, 0);
> > +       else
> > +               pinctrl_late_init(&pctldev->late_init.work);
> >
> >         return pctldev;

We could also pass some flag if should always call pinctrl_late_init()
directly. But that does not remove the problem of struct pinctrl_dev handle
being uninitialized when the pin controller driver functionas are called.

Regards,

Tony