linux-kernel - Re: RFC: gpio: mmio: add support for 3 direction regs

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Date:   Thu, 3 Jan 2019 10:07:11 +0200
From:   Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
To:     "Fried, Ramon" <ramon.fried@...ux.intel.com>,
        <linus.walleij@...aro.org>, <bgolaszewski@...libre.com>,
        <linux-gpio@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>,
        <vladimir.kondratiev@...ux.intel.com>
Subject: Re: RFC: gpio: mmio: add support for 3 direction regs

Hi Ramon,

On 01/03/2019 09:36 AM, Fried, Ramon wrote:
> Hi.
> 
> I'm working on a driver for STA2X11 GPIO controller who seems to fit
> best to the generic mmio driver,

I hope you have seen the existing driver drivers/gpio/gpio-sta2x11.c

> the only problem I have is with the dir register case. The STA2X11
> has 3 registers for dir, one for data, one for set and one for
> clear. The generic-mmio driver has support for this fashion for the
> dat & set & clear registers but not for dirout/dirin registers.
> 
> I wonder if support for this is generic enough to deserve a patch, if
> so I'm willing to quickly add this support, if not, adding a flag
> such as below, will allow partly using the generic mmio driver only
> for set/get and the direction can be handled outside the driver.
> 

If gpio-mmio fits well, then it might be simpler to set a flag
BGPIOF_UNREADABLE_REG_DIR, then call bgpio_init() and then overwrite
.direction_input, .direction_output and .get_direction callbacks,
as a reference you can take a look at gpio-74xx-mmio.c

--
Best wishes,
Vladimir