[i2c] [PATCH] Lifebook apanel driver

Vojtech Pavlik vojtech at suse.cz
Thu Jan 11 10:43:40 CET 2007


On Thu, Jan 11, 2007 at 10:38:55AM +0100, Jean Delvare wrote:

> > > I do see errors occurring (I think it is related to some power saving).
> > > So new version doesn't stop until errors occur for 2 seconds of polling.
> > 
> > Most likely ACPI is also accessing SMBus and there is no locking to
> > prevent collisions.
> 
> This seems to happen on more and more laptops unfortunately :( It's a
> shame that ACPI is accessing I/O resources without requesting them.

Windows doesn't touch SMBus itself. So BIOS vendors don't care about the
semaphore. But still, the buttons work in Windows, so it's done in some
way, most likely using some not much documented ACPI interface (not the
generic button one).

> The Intel 82801 SMBus has a hardware semaphore which could be used to
> prevent concurrent accesses, but I've neved seen a BIOS using it, and
> our i2c-i801 driver doesn't use it either at the moment. Of course it
> can only work if everyone plays the game.

Any feature Windows doesn't need cannot be relied upon to be working
correctly. That's the case on recent notebooks. Even Vista doesn't work
well on many of them, as they were ever tested only with XP.

-- 
Vojtech Pavlik
Director SuSE Labs



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