linux-kernel - Re: [PATCH 1/2] gpio: Add a driver for Cadence GPIO controller

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Date:   Fri, 31 Mar 2017 15:28:22 +0200
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     Simon Hatliff <hatliff@...ence.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Alexandre Courbot <gnurou@...il.com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Subject: Re: [PATCH 1/2] gpio: Add a driver for Cadence GPIO controller

On Thu, 30 Mar 2017 18:26:01 +0100
Simon Hatliff <hatliff@...ence.com> wrote:


> > Another solution would be to write 0xffffffff into CDNS_GPIO_OUTPUT_EN
> > at probe time so that each time CDNS_GPIO_DIRECTION_MODE is modified to
> > set a pin in output mode, the CDNS_GPIO_OUTPUT_EN is already correctly
> > configured.
> > Simon, would that work? Is there a good reason to keep a bit in
> > CDNS_GPIO_OUTPUT_EN set to 0 when the GPIO is in input mode (power
> > consumption?)?  
> If direction_mode is set to input then output_en is ignored so this 
> should work.  The hardware defaults to output mode, so as long as you 
> set all pins to input mode before you set all output_en bits there 
> should be no negative effect.

Okay, I'll try something like that, except I'll probably keep already
output-enabled in their existing state to avoid modifying bootloader's
GPIO settings.

Thanks for the feedback.

Boris