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

[Stephen Warren]

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.

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.