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

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Date:	Fri, 23 Oct 2015 06:51:28 -0500
From:	Rob Herring <robh+dt@...nel.org>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	Ray Jui <rjui@...adcom.com>, 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 Fri, Oct 23, 2015 at 4:08 AM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> 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.

Rob
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