linux-kernel - Re: [PATCH v3] gpio: add GPIO support for F71882FG and F71889F

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Message-ID: <521F4F95.5080103@roeck-us.net>
Date:	Thu, 29 Aug 2013 06:41:41 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Matthew Garrett <mjg59@...f.ucam.org>
CC:	Linus Walleij <linus.walleij@...aro.org>,
	Simon Guinot <simon.guinot@...uanux.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Grant Likely <grant.likely@...retlab.ca>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: [PATCH v3] gpio: add GPIO support for F71882FG and F71889F

On 08/29/2013 05:57 AM, Matthew Garrett wrote:
> On Thu, Aug 29, 2013 at 02:39:33PM +0200, Linus Walleij wrote:
>
>> I think Rafael said something about it being possible for us
>> to register our own kernel ACPI PNP IDs (as if: there is no
>> road here, but if someone starts to walk here, a road will
>> soon become, and we take the first step then).
>
> It'd be straightforward to register the LNX PnP prefix and have someone
> take responsibility for assigning numbers, but really a generic vendor
> string should only be used when defining programming models rather than
> specific devices.
>
>> But overall I am a bit confused: I am hearing from one end
>> of the x86 community that ACPI is the way to go for
>> configuring platform devices on x86, yet stuff like this is
>> popping up from independent vendors, and get integrated
>> on boards with no ACPI tables in sight.
>
> ACPI is usually used to describe systems, and the normal ACPI way of
> handling GPIO devices is to expose the device at the other end of the
> GPIO lines and then provide AML for toggling the lines. Attaching an
> actual driver to the device would interfere with that, so nobody writes
> an actual driver.
>
>> Over at ksummit-discuss we have had a thread about
>> whether device tree should be used in such cases, but
>> that is not clear either.
>
> If a vendor doesn't provide any way to autoprobe a device, there's no
> way to autoprobe a device. That usually means that you're not expected
> to use that device.
>

Pretty radical. Following your advice, should we remove all watchdog
and hwmon drivers for all SuperIO chips out there, plus any existing
gpio drivers (drivers/char/pc8736x_gpio.c might be a candidate) ?

Oh, and the parallel port driver also detects super-io chips directly,
so maybe the respective code should be removed as well. I am sure there
is more code that can be removed.

Or is the idea to say "no acpi, no new driver" ? Just wondering -
I have a GPIO driver for Nuvoton chips on my back-burner; that would be
necessary to access some fan controls connected to gpio pins on some boards.
If this is a no-go, I'll happily drop it from my list of things to do,
and just tell the user community that Linux won't support their hardware
due to policy reasons.

Guenter

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