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

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Message-ID: <559FFBCF.4020906@wwwdotorg.org>
Date:	Fri, 10 Jul 2015 11:07:27 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
CC:	Rob Herring <robherring2@...il.com>,
	"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 07/10/2015 10:21 AM, Tomeu Vizoso wrote:
> On 10 July 2015 at 17:27, Stephen Warren <swarren@...dotorg.org> wrote:
>> On 07/10/2015 03:29 AM, Tomeu Vizoso wrote:
>>>
>>> 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.
>>
>>
>> That doesn't make sense; the mapping between GPIO controller pins and pin
>> controller pins is a property of the SoC not the board.
>
>  From what Rob said above, apparently some boards will rely on the pin
> setup done by the bootloader, and some other boards with the same soc
> will want to do it in the kernel. So it's not really a difference in
> the hw itself, but what expectations exist about the firmware on a
> specific board.

Sure, but none of that changes the mapping between the GPIO and pin 
controller pins.

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