linux-kernel - Re: [PATCH v1 1/3] gpio: defer probe if pinctrl cannot be found

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Message-ID: <CAAObsKBS0OOhPNEAEV5Bh_+WMVWYhuGtGLqaVdCbzxPuT8a_gA@mail.gmail.com>
Date:	Fri, 10 Jul 2015 11:29:25 +0200
From:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:	Rob Herring <robherring2@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Alexandre Courbot <gnurou@...il.com>
Subject: Re: [PATCH v1 1/3] gpio: defer probe if pinctrl cannot be found

On 1 July 2015 at 19:36, Rob Herring <robherring2@...il.com> wrote:
> On Wed, Jul 1, 2015 at 7:45 AM, Tomeu Vizoso <tomeu.vizoso@...labora.com> wrote:
>> When an OF node has a pin range for its GPIOs, return -EPROBE_DEFER if
>> the pin controller isn't available.
>>
>> Otherwise, the GPIO range wouldn't be set at all unless the pin
>> controller probed always before the GPIO chip.
>>
>> With this change, the probe of the GPIO chip will be deferred and will
>> be retried at a later point, hopefully once the pin controller has been
>> registered and probed already.
>
> This will break cases where the pinctrl driver does not exist, but the
> DT contains pinctrl bindings. We can have similar problems already
> with clocks though. However, IMO this problem is a bit different in
> that pinctrl is more likely entirely optional while clocks are often
> required. You may do all pin setup in bootloader/firmware on some
> boards and not others. Of course then why put pinctrl in the DT in
> that case? They could be present just due to how chip vs. board dts
> files are structured.

I see. My instinct tells me that it would be better if the gpio-ranges
property was set in the board dts, but I don't really know what each
mach does with its DTSs.

> We could address this by simply marking the pin controller node
> disabled. However, ...
>
>> @@ -361,7 +361,7 @@ static void of_gpiochip_add_pin_range(struct gpio_chip *chip)
>>
>>                 pctldev = of_pinctrl_get(pinspec.np);
>>                 if (!pctldev)
>> -                       break;
>> +                       return -EPROBE_DEFER;
>
> But you cannot distinguish that case here. I think of_pinctrl_get
> needs to set the error code appropriately.

Why not? I was thinking of just doing this before we call of_pinctrl_get():

        if (!of_device_is_available(pinspec.np))
            continue;

Thanks,

Tomeu

> Rob
> --
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