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

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Date:	Fri, 10 Jul 2015 18:21:10 +0200
From:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:	Stephen Warren <swarren@...dotorg.org>
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 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.

Regards,

Tomeu
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