linux-kernel - Re: [PATCH 3/5] gpio: msc313: MStar MSC313 GPIO driver

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Date:   Thu, 5 Nov 2020 10:21:27 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Daniel Palmer <daniel@...f.com>
Cc:     "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/5] gpio: msc313: MStar MSC313 GPIO driver

On Wed, Oct 21, 2020 at 1:07 PM Daniel Palmer <daniel@...f.com> wrote:

> Sorry to pester you again...

Don't worry. I'm more worried that my replies are slow.

> Before I do that I have a question that maybe you could help me with:
> Andy noted a few times that I have this driver as a built in driver
> and not a module.
> The gpio-ixp4xx.c driver is also a built in driver. Is there a reason
> why it's ok there but not this driver?

Not that I know of. There is a lot of push for modularization right
now because Android (and other distributions) likes it, so if your
SoC could be used by Android or Fedora or Debian etc it is
generally a good idea to modularize.

These distributions use the generic ARM (etc) kernel and try
to load as many drivers as possible as modules.

It is not always possible because some GPIOs might be needed
very early, such as on-chip GPIO. So you better make sure
that the platform can get to userspace also without this driver
compiled in, otherwise it *MUST* be bool so people don't get
ammunition to shoot themselves in the foot and configure a
non-bootable kernel just because they could modularize this
driver.

If your SoC is only used by OpenWrt (like ixp4xx) then it is fine
to just use bool because that distribution is always built with an
image for a specific hardware, whereas distributions are generic.

So it actually depends a bit on the usecase of the SoC.

Yours,
Linus Walleij