linux-kernel - Re: [PATCH 2/2] hwmon: Allow to compile dell-smm-hwmon driver without /proc/i8k

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Date:	Mon, 30 Mar 2015 09:44:29 +0200
From:	Jean Delvare <jdelvare@...e.de>
To:	Pali Rohár <pali.rohar@...il.com>
Cc:	Steven Honeyman <stevenhoneyman@...il.com>,
	Paul Bolle <pebolle@...cali.nl>,
	Guenter Roeck <linux@...ck-us.net>,
	Arnd Bergmann <arnd@...db.de>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Jochen Eisinger <jochen@...guin-breeder.org>,
	Gabriele Mazzotta <gabriele.mzt@...il.com>,
	linux-kernel@...r.kernel.org, lm-sensors@...sensors.org
Subject: Re: [PATCH 2/2] hwmon: Allow to compile dell-smm-hwmon driver
 without /proc/i8k

On Sat, 28 Mar 2015 23:33:46 +0100, Pali Rohár wrote:
> I think it would be better to locate on which bus are sensors 
> connected (smbus? isa? pci?), find out HW chips and wrote native 
> kernel drivers for them...
> 
> I scanned smbus (intel controller connected on pci) on my E6440 
> but there is no additional/unknown device. I have no idea where 
> else could be sensor device connected and accessible (from SMM or 
> kernel mode).

As much as I hate SMM, native access to a BIOS-owned device is not a
good idea, as is it dangerously racy. If anything, we are currently
trying to move _away_ from native drivers on a number of systems
(basically all systems where acpi_enforce_resources=lax is needed.)

On x86, ideally ACPI would offer a standard interface to the hardware
monitoring chip and the OS would need a single driver for all boards
out there. Failing that, ACPI should provide a clean and safe way to
access the chip's registers (read: some mutex to avoid concurrent
access to the registers by the BIOS and the OS.)

-- 
Jean Delvare
SUSE L3 Support
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