linux-kernel - Re: [PATCH 4/5] gpio: of: Add support to have multiple gpios in gpio-hog

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Date:	Thu, 10 Mar 2016 12:37:32 +0530
From:	Laxman Dewangan <ldewangan@...dia.com>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	Markus Pargmann <mpa@...gutronix.de>, <linus.walleij@...aro.org>,
	<robh+dt@...nel.org>, <pawel.moll@....com>, <mark.rutland@....com>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-gpio@...r.kernel.org>, <treding@...dia.com>,
	Benoit Parrot <bparrot@...com>,
	Alexandre Courbot <acourbot@...dia.com>
Subject: Re: [PATCH 4/5] gpio: of: Add support to have multiple gpios in gpio-hog


On Wednesday 09 March 2016 10:47 PM, Stephen Warren wrote:
> On 03/09/2016 06:20 AM, Laxman Dewangan wrote:
>>
>> On Wednesday 09 March 2016 11:58 AM, Markus Pargmann wrote:
>>> * PGP Signed by an unknown key
>>>
>>> Hi,
>>>
>>> On Tue, Mar 08, 2016 at 05:32:07PM +0530, Laxman Dewangan wrote:
>>>> The child node for gpio hogs under gpio controller's node
>>>> provide the mechanism to automatic GPIO request and
>>>> configuration as part of the gpio-controller's driver
>>>> probe function.
>>>>
>>>> Currently, property "gpio" takes one gpios for such
>>>> configuration. Add support to have multiple GPIOs in
>>>> this property so that multiple GPIOs of gpio-controller
>>>> can be configured by this mechanism with one child node.
>>> So if I read this correctly you want to have multiple GPIOs with the
>>> same line name? Why don't you use multiple child nodes with individual
>>> line names?
>>>
>> There is cases on which particular functional configuration needs sets
>> of GPIO to set. On this case, making sub node for each GPIOs creates
>> lots of sub-nodes and  add complexity on readability, usability and
>> maintainability.
>> Example: for my board, I wanted to set GPIO H2 to input and H0 and H1 to
>> be output high.
>> Instead of three nodes, I can have two here:
>>         gpio@0,6000d000 {
>>                 wlan_input {
>>                         gpio-hog;
>>                         gpios = <TEGRA_GPIO(H, 2) 0>;
>>                         input;
>>                 };
>>
>>                 wlan_output {
>>                         gpio-hog;
>>                         gpios = <TEGRA_GPIO(H, 0) 0 TEGRA_GPIO(H, 1) 0>;
>>                         output-high;
>>                 };
>>         };
> >
>> So here I am grouping the multiple output GPIO together.
>>
>> This looks much similar if we have many GPIOs for one type of
>> configurations.
>>
>> Even it looks better if we have something:
>>         gpio@0,6000d000 {
>>                 wlan_control {
>>                         gpio-hog;
>>                         gpios-input = <TEGRA_GPIO(H, 2) 0>;
>>                         gpios-output-high = <TEGRA_GPIO(H, 0) 0
>> TEGRA_GPIO(H, 1) 0>;
>>                 };
>>         };
>
> The problem with that is the description used when acquiring the GPIO 
> is just "wlan_input", "wlan_output", or "wlan_control". There's 
> nothing to indicate what those individual pins do (perhaps one is a 
> reset signal, one is a regulator enable, etc.?) By requiring separate 
> nodes for each GPIO, then the node name can provide a meaningful 
> semantic name/description for each GPIO, which provides much more 
> information.
>

On this case, we have already property "line-name" and passed the name 
of the gpio via this property.
The property names is "line-name" which is good for one string. We can 
support other property "line-names" with multiple string per GPIO index.

line-names = "wlan-reset", "wlan-enable";


> If the approach in this patch is acceptable though, I think you want 
> to update the description of "gpios" (in the GPIO hog definition 
> section) in Documentation/devicetree/bindings/gpio/gpio.txt to mention 
> that multiple GPIO entries are legal. Right now it says that property 
> much contain exactly #gpio-cells, not a multiple of #gpio-cells.

I have 5th patch for this and will rearrange series as you suggested on 
5th patch.