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

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Date:	Fri, 23 Oct 2015 12:08:50 +0300
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Rob Herring <robh+dt@...nel.org>
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 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 ?

-- 
Regards,

Laurent Pinchart

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