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Date:   Tue, 23 Jun 2020 14:47:28 +0200
From:   Michael Walle <michael@walle.cc>
To:     Sungbo Eo <mans0n@gorani.run>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        linux-kernel@vger.kernel.org, linux-gpio@vger.kernel.org
Subject: Re: [PATCH] gpio: add GPO driver for PCA9570
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 <2291c01d-30df-518e-a952-644bd955f1f3@gorani.run>
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Hi Sungbo,

Am 2020-06-23 14:22, schrieb Sungbo Eo:
> On 2020-06-23 17:31, Michael Walle wrote:
>> Am 2020-06-23 08:05, schrieb Sungbo Eo:
>>> This patch adds support for the PCA9570 I2C GPO expander.
>>> 
>>> Signed-off-by: Sungbo Eo <mans0n@gorani.run>
>>> ---
>>> Tested in kernel 5.4 on an ipq40xx platform.
>>> 
>>> This is my first time submitting a whole driver patch, and I'm not
>>> really familiar with this PCA expander series.
>>> Please let me know how I can improve this patch further. (Do I also
>>> need to document the DT compatible string?)
>> 
>> Did you have a look at drivers/gpio/gpio-regmap.c ? Your driver seems
>> to be simple enough to be easily integrated with that. If you need a
>> blueprint; because at the moment there is no driver in the kernel
>> using that, you could have a look at:
>> https://lore.kernel.org/linux-gpio/20200604211039.12689-7-michael@walle.cc/
> 
> Thanks for your advice. I didn't really know what regmap is for...
> It seems gpio-regmap is for gpio controllers having val/dir registers.
> But pca9570 does not use port registers. The master only sends a data
> byte without reg address.

Ahh I missed that :(

> I'm not sure how to apply gpio-regmap or
> regmap-i2c here.
> I'll try to investigate if setting reg_size or reg_bits to zero is 
> possible.
> 
> Please correct me if I'm in the wrong direction.

That won't work because the underlying regmap expects the address bits 
to be either 8 or 16. In this case I'd guess gpio-regmap, doesn't make 
sense, because there is actually no real gain.

-michael