linux-kernel - Re: [PATCH] gpio: add GPO driver for PCA9570

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Message-ID: <83f1fba7fb04780b84c5e96a184f61f9@walle.cc>
Date:   Sat, 27 Jun 2020 18:58:54 +0200
From:   Michael Walle <michael@...le.cc>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Sungbo Eo <mans0n@...ani.run>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH] gpio: add GPO driver for PCA9570

Hi,

Am 2020-06-24 16:52, schrieb Andy Shevchenko:
> On Wed, Jun 24, 2020 at 4:46 PM Michael Walle <michael@...le.cc> wrote:

[..]

>> So you just write one byte of data (or you might repeat it, but
>> that is just as if you start a new i2c transaction, just that
>> you save the i2c addressing).
> 
> You can write the same value twice.
> It means that the first byte can represent the register address. But
> it's still too volatile.

In this case the output pin will hold the value of the "fake" address
register for a short period of time. No?

> Perhaps regmap can gain something like register-less communication.

I don't know if that is worth it (and if that is an intended use of
regmap).

-michael