From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Anholt <eric-WhKQ6XTQaPysTnJN9+BGXg@public.gmane.org>
Subject: Re: [PATCH 27/32] gpio: Add support for the FXL6408 GPIO expander.
Date: Thu, 09 Jun 2016 10:22:27 -0700
Message-ID: <878tyexooc.fsf@eliezer.anholt.net>
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To: Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>, Gerd Hoffmann <kraxel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: linux-rpi-kernel <linux-rpi-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>, Florian Fainelli <f.fainelli-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Ray Jui <rjui-dY08KVG/lbpWk0Htik3J/w@public.gmane.org>, Scott Branden <sbranden-dY08KVG/lbpWk0Htik3J/w@public.gmane.org>, Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Pawel Moll <pawel.moll-5wv7dgnIgG8@public.gmane.org>, Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>, Ian Campbell <ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org>, Kumar Gala <galak-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>, Catalin Marinas <catalin.marinas-5wv7dgnIgG8@public.gmane.org>, Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>, Alexandre Courbot <gnurou-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, "open list:BROADCOM BCM281XX/BCM11XXX/BCM216XX ARM ARCHITE..." <bcm-kernel-feedback-list-dY08KVG/lbpWk0Htik3J/w@public.gmane.org>, "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" <devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" <linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>, open list <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, "open list:GPIO SUBSYSTEM" <linux-gpio-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
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Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> writes:

> On Wed, Jun 1, 2016 at 11:43 PM, Gerd Hoffmann <kraxel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
>
>> +#define FXL6408_OUTPUT                 0x05
>> +/* Bits here make the output High-Z, instead of the OUTPUT value. */
>> +#define FXL6408_OUTPUT_HIGH_Z          0x07
> (...)
>> +       /* Disable High-Z of outputs, so that our OUTPUT updates
>> +        * actually take effect.
>> +        */
>> +       i2c_smbus_write_byte_data(client, FXL6408_OUTPUT_HIGH_Z, 0);
>
> High-Z is probably the same as open drain right? And if not open drain,
> it is push-pull.
>
> So you want to implement .set_single_ended() for configuring the lines in
> "high-z", i.e. open drain output mode.

I'll keep this in mind for whenever I end up writing my next GPIO
driver, but this one is dead for now (not actually usable because of the
closed firmware).

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