Re: [PATCH] gpio: add GPO driver for PCA9570

[Sungbo Eo]

On 2020-06-24 22:01, Andy Shevchenko wrote:
> On Tue, Jun 23, 2020 at 9:06 AM Sungbo Eo <mans0n@xxxxxxxxxx> 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...)