Re: [PATCH] gpio:pca953x: add mechanism to simulate open drain outputs

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Wed, Sep 23, 2015 at 11:13 AM, H. Nikolaus Schaller
<hns@xxxxxxxxxxxxx> wrote:

> 1. add a DT property to specify the list of GPIO pins that are to become
>    "open drain"
> 2. if a pin is configured as "open drain", set value by either outputting a
>    "0" (low level) or switching to input (high impedance)
>
> Tested on OMAP5 uEVM with TCA6424 and some LEDs connected to 5V.
>
> Signed-off-by: H. Nikolaus Schaller <hns@xxxxxxxxxxxxx>

I understand the approach, but this is the wrong way to do it.
Instead of indicating that a pin on the pin controller should be
open drain, the *consumer* specifying its gpios = <....> should
do this.

I just sent a patch adding the bindings because Tony Lindgren
and Grygorii Strashko approached me similar problems so let's
begin with the bindings.

Implementing it in the kernel requires some elaboration and it's
going to be more complicated than this local approach, but it
will be more generic and reusable so that is what we need to do.

Yours,
Linus Walleij
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