linux-kernel - Re: [RFC] Potential issue with GPIO/IRQ flags

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Date:	Thu, 17 Sep 2015 15:35:08 -0700
From:	Stephen Warren <swarren@...dia.com>
To:	"Andrew F. Davis" <afd@...com>, Rob Herring <robh@...nel.org>
Cc:	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Andreas Fenkart <afenkart@...il.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [RFC] Potential issue with GPIO/IRQ flags

On 09/17/2015 11:21 AM, Andrew F. Davis wrote:
> 
> 
> On 09/17/2015 12:20 PM, Rob Herring wrote:
>> On Thu, Sep 17, 2015 at 10:53 AM, Andrew F. Davis <afd@...com> wrote:
>>> On 09/16/2015 08:26 PM, Rob Herring wrote:
>>>>
>>>> On Wed, Sep 16, 2015 at 4:07 PM, Andrew F. Davis <afd@...com> wrote:
>>>>>
>>>>> Hello all,
>>>>>
>>>>> I've noticed that in a few DT bindings GPIO_ACTIVE_* defines are
>>>>> incorrectly used as interrupt flags. GPIO_ACTIVE_*'s are defined
>>>>> in:
>>>>>
>>>>> include/dt-bindings/gpio/gpio.h
>>>>>
>>>>> and are used to describe GPIO pins. IRQ types are defined in:
>>>>>
>>>>> include/dt-bindings/interrupt-controller/irq.h
>>>>>
>>>>> and are flags for IRQ pins.
>>>>
>>>>
>>>> It is perfectly valid for the meaning of the field to be defined by
>>>> the interrupt controller, and gpio interrupts could do something
>>>> different. We've tried to standardize this though.
>>>>
>>>
>>> Sure, but in this case these are not what the interrupt controller
>>> is expecting.
>>
>> Understood. I was talking generally, not this specific case.
>>
>>>>> These seem to have been mixed up in a few places, take for example:
>>>>> arch/arm/boot/dts/tegra124-jetson-tk1.dts. On line 1393 we see the
>>>>> correct usage, but just before on line 1384 we see the issue.
>>>>> GPIO_ACTIVE_HIGH is defined as 0, the same as IRQ_TYPE_NONE. If
>>>>> this IRQ was not hard-coded with the correct edge in the driver
>>>>> this would not work. What the author probably wanted was
>>>>> IRQ_TYPE_LEVEL_HIGH.
>>>>>
>>>>> Now lets look at commit c21e678b256b, in this the IRQ flags did not
>>>>> matter as the correct flag was hard-coded (IRQF_TRIGGER_LOW), this
>>>>> patch moves this to the DT, but changed the flag to GPIO_ACTIVE_LOW
>>>>> instead of the desired IRQ_TYPE_LEVEL_LOW. GPIO_ACTIVE_LOW is defined
>>>>> as 1, or IRQ_TYPE_EDGE_RISING in IRQ flags, which is not the
>>>>> equivalent to IRQF_TRIGGER_LOW the author was probably looking for.
>>>>>
>>>>> A quick grep (git grep "interrupt.*GPIO_ACTIVE_") shows several more
>>>>> instances of this. I found this by using one of these files as an
>>>>> example and giving myself a lot of problems, so I would like to fix
>>>>> this before it spreads anymore.
>>>>>
>>>>> I have a couple of ideas of how to go at this, first would be to
>>>>> just replace the incorrect flags with what was intended, but for
>>>>> some of these I don't know what was intended and do not have the
>>>>> board to test.
>>>>>
>>>>> My other solution would be to just change all instances of the GPIO
>>>>> flags to their value corresponding IRQ flags:
>>>>>
>>>>> - interrupts = <11 GPIO_ACTIVE_LOW>;
>>>>> + interrupts = <11 IRQ_TYPE_EDGE_RISING>;
>>>>>
>>>>> this would not make any functional change as the defines would
>>>>> still evaluate to the same value, but would make it obvious where
>>>>> a problem may be and that they should probably be checked and
>>>>> corrected, maybe we could even put a comment after:
>>>>>
>>>>> - interrupts = <11 GPIO_ACTIVE_LOW>;
>>>>> + interrupts = <11 IRQ_TYPE_EDGE_RISING>; // FIXME: Check IRQ type
>>>>>
>>>>> Well, what do you think?
>>>>
>>>>
>>>> This seems fine. It is no less wrong.
>>>>
>>>
>>> I'm not sure what you mean here.
>>
>> In this example, the correct value is probably IRQ_TYPE_LEVEL_LOW or
>> IRQ_TYPE_EDGE_FALLING if the original text was correct in its
>> intentions (but broken in implementation). Since the change you
>> propose doesn't change the actual dtb at all, if it was wrong before
>> it will still be wrong.
>>
> 
> I see, that's kinda what I want, maybe for this example the intentions
> are obvious but my concern is with a couple others that I don't know
> what the trigger was meant to be and don't have a board to test the
> changes with, so I would never be sure if I causing any regressions
> with the fixes. Most of the affected boards are Tegra based (that's
> why I cc'd linux-tegra), I was hoping they would be interested in
> testing and finding the right values.

Presumably/hopefully if you send specific patches, the various
maintainers/owners of those DT files will validate/ack then; you don't
need to be able to test all of the changes yourself.
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