linux-kernel - Re: [PATCH v2 1/6] gpio: i8255: Introduce the i8255 module

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Date:   Mon, 11 Jul 2022 23:06:39 -0400
From:   William Breathitt Gray <william.gray@...aro.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     brgl@...ev.pl, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org, Fred Eckert <Frede@...laser.com>,
        John Hentges <jhentges@...esio.com>,
        Jay Dolan <jay.dolan@...esio.com>
Subject: Re: [PATCH v2 1/6] gpio: i8255: Introduce the i8255 module

On Mon, Jul 11, 2022 at 03:02:10PM +0200, Linus Walleij wrote:
> On Fri, Jul 8, 2022 at 1:16 AM William Breathitt Gray
> <william.gray@...aro.org> wrote:
> 
> > Exposes consumer functions providing support for Intel 8255 Programmable
> > Peripheral Interface devices. A CONFIG_GPIO_I8255 Kconfig option is
> > introduced; modules wanting access to these functions should select this
> > Kconfig option.
> >
> > Tested-by: Fred Eckert <Frede@...laser.com>
> > Cc: John Hentges <jhentges@...esio.com>
> > Cc: Jay Dolan <jay.dolan@...esio.com>
> > Signed-off-by: William Breathitt Gray <william.gray@...aro.org>
> 
> This chip is like 50 years old, but so am I and I am not obsolete, it's about
> time that we implement a proper driver for it!
> 
> But I suppose you are not really using the actual discrete i8255 component?
> This is certainly used as integrated into some bridge or so? (Should be
> mentioned in the commit.)

Interestingly, there are some PC/104 devices out there that use actual
i8255 components (e.g. Diamond Systems Onyx-MM with its 82C55 chips),
but honestly the majority of devices I come across are simply emulating
the i8255 interface in an FPGA or similar.

I'll adjust the commit to make it clearer that this is a library for
i8255-compatible interfaces rather than support for any physical Intel
8255 chip in particular.

> > +config GPIO_I8255
> > +       tristate
> 
> That's a bit terse :D Explain that this is a Intel 8255 PPI chip first developed
> in the first half of the 1970ies.

Ack.

> > +++ b/include/linux/gpio/i8255.h
> 
> You need to provide a rationale for the separate .h file in the commit
> message even if it is clear
> how it is used in the following patches.
> 
> Yours,
> Linus Walleij

I think I'll move this to gpio/driver.h as per Andy Shevchenko's
suggestion. For now only a few drivers under drivers/gpio/ use this
library, so it probably doesn't need to be separate just yet.

William Breathitt Gray

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