linux-kernel - Re: [PATCH 05/11] dt-binding: Add ngpios property to GPIO controller node

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Message-ID: <562A5B75.7010804@broadcom.com>
Date:	Fri, 23 Oct 2015 09:08:21 -0700
From:	Ray Jui <rjui@...adcom.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Rob Herring <robh+dt@...nel.org>
CC:	Pramod Kumar <pramodku@...adcom.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"Scott Branden" <sbranden@...adcom.com>,
	Russell King <linux@....linux.org.uk>,
	Linus Walleij <linus.walleij@...aro.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
	Jason Uy <jasonuy@...adcom.com>,
	Masahiro Yamada <yamada.masahiro@...ionext.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jonas Gorski <jogo@...nwrt.org>
Subject: Re: [PATCH 05/11] dt-binding: Add ngpios property to GPIO controller
 node



On 10/23/2015 6:02 AM, Laurent Pinchart wrote:
> Hi Rob,
>
> On Friday 23 October 2015 06:51:28 Rob Herring wrote:
>> On Fri, Oct 23, 2015 at 4:08 AM, Laurent Pinchart wrote:
>>> On Thursday 22 October 2015 18:41:05 Rob Herring wrote:
>>>> On Thu, Oct 22, 2015 at 1:52 PM, Ray Jui wrote:
>>>>> On 10/22/2015 11:43 AM, Rob Herring wrote:
>>>>>> On Mon, Oct 19, 2015 at 12:43 AM, Pramod Kumar wrote:
>>>>>>> Add ngpios property to the gpio controller's DT node so that
>>>>>>> controller driver extracts total number of gpio lines present in
>>>>>>> controller from DT and removes dependency on driver.
>>>>>>>
>>>>>>> Signed-off-by: Pramod Kumar <pramodku@...adcom.com>
>>>>>>> Reviewed-by: Ray Jui <rjui@...adcom.com>
>>>>>>> Reviewed-by: Scott Branden <sbranden@...adcom.com>
>>>>>>> ---
>>>>>>>
>>>>>>>   Documentation/devicetree/bindings/pinctrl/brcm,cygnus-gpio.txt | 5
>>>>>>>   +++
>>>>>>>   1 file changed, 5 insertions(+)
>>>>>>>
>>>>>>> diff --git
>>>>>>> a/Documentation/devicetree/bindings/pinctrl/brcm,cygnus-gpio.txt
>>>>>>> b/Documentation/devicetree/bindings/pinctrl/brcm,cygnus-gpio.txt
>>>>>>> index f92b833..655a8d7 100644
>>>>>>> --- a/Documentation/devicetree/bindings/pinctrl/brcm,cygnus-gpio.txt
>>>>>>> +++ b/Documentation/devicetree/bindings/pinctrl/brcm,cygnus-gpio.txt
>>>>>>>
>>>>>>> @@ -10,6 +10,9 @@ Required properties:
>>>>>>>        Define the base and range of the I/O address space that
>>>>>>>        contains
>>>>>>>
>>>>>>> the Cygnus
>>>>>>>
>>>>>>>    GPIO/PINCONF controller registers
>>>>>>>
>>>>>>> +- ngpios:
>>>>>> +    Total number of GPIOs the controller provides
>>>>>>
>>>>>> This must be optional for compatibility and the driver needs to handle
>>>>>> it not present.
>>>>>
>>>>> You meant to be compatible with existing Cygnus devices, correct?
>>>>>
>>>>> Just to clarify, here you suggest we still leave the existing hard
>>>>> coded ngpios in the driver, in order to be compatible with all existing
>>>>> Cygnus devices (while the Cygnus device tree changes to use ngpio is
>>>>> still being merged and through different maintainer), and have all new
>>>>> iProc SoCs switch to use ngpios from device tree, right?
>>>>
>>>> Yes, an existing dtb should continue to work with a new kernel. You
>>>> can add the DT property to the older devices too and then eventually
>>>> remove the hard coded values some time in the future. That could be
>>>> immediately (don't care about compatibility at all), a couple of
>>>> kernel cycles, never... It all depends on users of the impacted
>>>> platforms.
>>>
>>> But shouldn't the property still be documented as required to ensure that
>>> new DTs always include it ?
>>
>> Good point. If the intent is to eventually remove it from the driver,
>> then yes. We probably need "required for new designs" as a category or
>> maybe "recommended"? The wording is not so important here, but I'm
>> thinking about as we try to standardize the naming.
>
> Required for new designs sounds better than recommended. Or maybe something
> like "Required (optional for backward compatibility)".
>

Yes, it should be phrased as "required for new designs" because all new 
iProc SoCs using this GPIO driver need to have this in DT.

Thanks,

Ray
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