linux-kernel - Re: [RFC] IT87xx GPIO and other drivers

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Date:	Mon, 16 Apr 2012 12:59:28 -0700
From:	Guenter Roeck <guenter.roeck@...csson.com>
To:	Diego Elio Pettenò <flameeyes@...meeyes.eu>
CC:	Grant Likely <grant.likely@...retlab.ca>,
	guillaume ligneul <guillaume.ligneul@...lis.com>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	Jean Delvare <khali@...ux-fr.org>,
	Wim Van Sebroeck <wim@...ana.be>,
	Denis Turischev <denis@...pulab.co.il>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>
Subject: Re: [RFC] IT87xx GPIO and other drivers

On Mon, 2012-04-16 at 15:51 -0400, Diego Elio Pettenò wrote:
> Hi all, sorry if I'm mailing lots of you at once, but I'm afraid I got
> my hands on a can of worms right now...
> 
> As some of you remember I've been working on a driver for supporting the
> GPIO functions of the IT8728F Super I/O chip, as well as making the WDT
> driver to work on this chip.
> 
> After trying to make a bit of sense of it all, I'm concerned that the
> only _correct_ way to handle this would be to ahve a set of drivers that
> work together, rather than a number of drivers that all do their own
> part. Currently we have:
> 
>  - hwmon/it87 which supports most it87xx chips;
>  - it87_wdt for most it87xx chips (including it8712);
>  - it8712f_wdt which supports the "Smart Guardian" watchdog;
>  - gpio_it8761e for that single IT87xx gpio;
>  - my gpio_it87 driver that works with it8728f and should work with
> it8761e (for what I can tell from the other driver), and Guillaume has
> code for IT8712 as well (which variant?).
> 
> What issues are there with this situation?
> 
> All these drivers use to some extent the Super I/O addresses (0x2e/0x2f)
> to read and write to its registers, including detection code which is
> replicated for each of them. The functions to read and write superio
> registers is also duplicate.
> 
> Only some of these drivers (namely gpio-it8761e for what I can tell)
> support checking both 0x2e/0x2f and 0x4e/0x4f, which is an alternative
> addressing for the superio register handling.
> 
> The GPIO pins on most of the it87xx chips are also multi-function, and
> _should not_ be user-visible, but for some of them it might make sense
> to (for instance it should be possible to drive some of the LEDs on
> it8728f-based motherboards by replacing the functions of some PINs to GPIO).
> 
> For what I can tell, it should probably be a good idea to have something
> along these lines, but I'm _not_ a driver expert:
> 
>  - mfd-it87xx: a platform driver, which probes the superio to check it
> to be an it87xx chip, and then reserve resources for the other drivers;
>  - hwmon/it87: no longer probes autonomously for which chip it is, and
> where it is;
>  - it87_wdt: ibidem;
>  - it8712_wdt: no clue about it, but I guess the same;
>  - gpio-it87: ibidem again;
>  - pinctrl-it87: abstracts support for the various pin-choice registers;
>  - led-it87: possibly to drive the power/network/hdd leds, akin to what
> happens with some laptops, and embedded systems.
> 
> Does a plan like this make sense? Denis have you still access to an
> it8761e board?
> 
Yes, that sounds about right.

Guenter


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