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

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Message-ID: <2291c01d-30df-518e-a952-644bd955f1f3@gorani.run>
Date:   Tue, 23 Jun 2020 21:22:32 +0900
From:   Sungbo Eo <mans0n@...ani.run>
To:     Michael Walle <michael@...le.cc>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org
Subject: Re: [PATCH] gpio: add GPO driver for PCA9570

Hi Michael,

On 2020-06-23 17:31, Michael Walle wrote:
> Hi Sungbo,
> 
> 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@...ani.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. 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.

Thanks.

> 
> -michael