linux-kernel - Re: [PATCH 02/21] ARM: tegra: Add gpio-ranges property

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Message-ID: <CAAObsKAkVKNOQpw9hbY-EVKjh7fRTfP5GbzcVVGxQMTFAztc7Q@mail.gmail.com>
Date:	Wed, 17 Jun 2015 12:04:53 +0200
From:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Stéphane Marchesin <stephane.marchesin@...il.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Alexander Holler <holler@...oftware.de>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Alexandre Courbot <gnurou@...il.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/21] ARM: tegra: Add gpio-ranges property

On 16 June 2015 at 22:32, Stephen Warren <swarren@...dotorg.org> wrote:
> On 06/16/2015 02:42 AM, Tomeu Vizoso wrote:
>>
>> On 2 June 2015 at 17:40, Stephen Warren <swarren@...dotorg.org> wrote:
>>>
>>> On 06/02/2015 05:28 AM, Linus Walleij wrote:
>>>>
>>>>
>>>> On Tue, May 26, 2015 at 9:41 PM, Stephen Warren <swarren@...dotorg.org>
>>>> wrote:
>>>>>
>>>>>
>>>>> On 05/25/2015 08:53 AM, Tomeu Vizoso wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>> Specify how the GPIOs map to the pins in T124, so the dependency is
>>>>>> explicit.
>>>>>>
>>>>>> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
>>>>>> ---
>>>>>>     arch/arm/boot/dts/tegra124.dtsi | 1 +
>>>>>>     1 file changed, 1 insertion(+)
>>>>>>
>>>>>> diff --git a/arch/arm/boot/dts/tegra124.dtsi
>>>>>> b/arch/arm/boot/dts/tegra124.dtsi
>>>>>> index 13cc7ca..5d1d35f 100644
>>>>>> --- a/arch/arm/boot/dts/tegra124.dtsi
>>>>>> +++ b/arch/arm/boot/dts/tegra124.dtsi
>>>>>> @@ -254,6 +254,7 @@
>>>>>>                   gpio-controller;
>>>>>>                   #interrupt-cells = <2>;
>>>>>>                   interrupt-controller;
>>>>>> +               gpio-ranges = <&pinmux 0 0 250>;
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> We should be consistent between SoCs. Why not make the same change for
>>>>> all
>>>>> Tegra SoCs?
>>>>
>>>>
>>>>
>>>> Agreed.
>>>>
>>>>> I think this change will cause the GPIO subsystem to call into the
>>>>> pinctrl
>>>>> subsystem and create/add/register a new GPIO<->pinctrl range structure.
>>>>> The
>>>>> pinctrl driver already does this, so I think we'll end up with two
>>>>> duplicate
>>>>> entries in the pinctrl device's gpio_ranges list. This probably won't
>>>>> cause
>>>>> a problem, but I wanted to make sure you'd thought about it to make
>>>>> sure.
>>>>
>>>>
>>>>
>>>> That sounds like duplication indeed, I would expect that first a patch
>>>> adds the ranges to the dts[i] files and then a second patch delete the
>>>> same ranges from the pinctrl driver then, if these shall come in from
>>>> the device tree.
>>>
>>>
>>>
>>> We can't delete the gpio-range-registration code from the Tegra pinmux
>>> driver, or old DTs won't work correctly. We could make it conditional
>>> based
>>> upon whether the DT contains the property or not.
>>
>>
>> I've been looking at this and haven't found a good solution. From what
>> I see, the pinctrl driver doesn't have a reference to the gpio device
>> node so cannot tell if it needs to add the range or not.
>
>
> Well, we know what the node must be called, so the pinctrl driver could
> search for it by name.

Ok, will write something in this direction.

>> The gpio driver can tell whether it should add the range or not, but
>> if it has to because the gpio-ranges property isn't there, then it
>> doesn't have the reference to the pinctrl device to set the range to.
>>
>> So, given that pinctrl_add_gpio_range is deprecated already, wonder if
>> the lesser evil isn't leaving the duplicated entries for now. On newer
>> SoC revisions such as T210 we can stop calling pinctrl_add_gpio_range
>> at all.
>>
>> Or, we can accept that nobody is going to boot a newer kernel with an
>> older DT on the affected boards and just rely on the presence of the
>> gpio-ranges property :)
>
>
> Isn't the simplest solution to just leave it as it is? Nothing's broken is
> it?

Well, without an explicit dependency from the gpio node to the pinctrl
node I cannot avoid a deferred probe (which will cause other deferred
probes in turn).

> For any new SoCs we add, we can certainly switch to a new scheme if we want,
> but we need to catch/implement that early before the base .dtsi file is
> included in its first kernel release.

Definitely.

Regards,

Tomeu

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