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

[Laxman Dewangan]

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.