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

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Date:   Thu, 25 Jun 2020 16:34:52 +0900
From:   Sungbo Eo <mans0n@...ani.run>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     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

On 2020-06-24 22:01, Andy Shevchenko wrote:
> On Tue, Jun 23, 2020 at 9:06 AM Sungbo Eo <mans0n@...ani.run> wrote:
>>
>> This patch adds support for the PCA9570 I2C GPO expander.
> 
>> 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?)
>>
>> FYI there's an unmerged patch for this chip.
>> http://driverdev.linuxdriverproject.org/pipermail/driverdev-devel/2017-May/105602.html
>> I don't have PCA9571 either so I didn't add support for it.
> 
> My very first questions to such (simple) driver submissions is: Have
> you conducted research of existing drivers and found that none is
> suitable for this chip?
> Do this and answer in a commit message, if it will be still valid.
> 

I've done a more extensive research for i2c expanders and found out that 
gw-pld, max732x, pcf857x also use i2c_smbus_write_byte() without reg 
address. But their architectures are more complex than pca9570 and I'm 
not sure if I can make them compatible with pca9570. (I still don't 
understand what "quasi-bidirectional" in pcf857x means...)