Re: I/O collisions w/ hwmon/it87.c and watchdog/it8712f_wdt.c? (Super I/O chips in general..)

[Jean Delvare <khali@linux-fr.org>]

Hi Andrew,

On Sun, 10 Feb 2008 16:04:25 -0500, Andrew Paprocki wrote:
> I'm interested in expanding the current support for the it87 Super I/O
> chip to provide access to more of its capabilities. I started by
> looking at two existing drivers which talk to different parts of the
> chip. Maybe I'm missing something, but what guarantees that both of
> these drivers won't attempt to talk to the chip at the same time?

Nothing guarantees it in general. However, at least most hwmon drivers
avoid accessing the Super-I/O configuration space after driver
initialization, which happens when the module is loaded. As module
loading is serialized, this limits the risk of concurrent access.

This is however a limitation I'd be happy to get rid of. It would be
nice to be able to access some configuration space registers at
run-time (e.g. VID readings).

> The watchdog/it8712f_wdt.c driver has an internal spinlock, the
> hwmon/it87.c driver doesn't, and I don't see how a lock could be
> shared across both unless it is taken care of at a lower level that
> I'm not aware of. You can see that code is essentially copied between
> the two files to talk to the chip.
> 
> This brings me to a more general question regarding SuperI/O chips.
> Since these chips touch many different parts of traditionally separate
> driver areas, how should the drivers be structured so that they can
> all talk to the chip? Should the low level communications routines for
> the chip live in a library which all the drivers could use? Should all
> of the created devices live inside one file? (e.g. platform/it87.c
> instead of hwmon, watchdog, etc)

You probably want to discuss this with Jim Cromie and Hans de Goede
(Cc'd.) They have been discussing a possible implementation in October
2007 on the lm-sensors list:

http://lists.lm-sensors.org/pipermail/lm-sensors/2007-October/021561.html
http://lists.lm-sensors.org/pipermail/lm-sensors/2007-October/021562.html
http://lists.lm-sensors.org/pipermail/lm-sensors/2007-October/021563.html
http://lists.lm-sensors.org/pipermail/lm-sensors/2007-October/021564.html
http://lists.lm-sensors.org/pipermail/lm-sensors/2007-October/021565.html
http://lists.lm-sensors.org/pipermail/lm-sensors/2007-October/021566.html

-- 
Jean Delvare