From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jean Delvare Subject: Re: Haswell systems & i801 i2c driver Date: Mon, 7 Apr 2014 22:56:20 +0200 Message-ID: <20140407225620.23d52a0c@endymion.delvare> References: <5342E7C0.4050209@redhat.com> <1396902638.5276.2.camel@x230> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1396902638.5276.2.camel@x230> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Matthew Garrett Cc: bhelgaas-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, jamorgan-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, rjw-LthD3rsA81gm4RdzfppkhA@public.gmane.org, seth.heasley-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, prarit-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, janet.morgan-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, mstowe-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, linux-acpi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-acpi@vger.kernel.org On Mon, 7 Apr 2014 20:30:39 +0000, Matthew Garrett wrote: > > If this is on a shipping BIOS, we might need to figure out some way to > > handle it. I don't remember anything in the ACPI spec that talks > > about issues like this, but maybe we should add something in PCI that > > notices if there's an ACPI device with the same resources and marks > > the PCI device to keep us from moving it or assigning a driver (maybe > > the warning you're seeing already handles the driver part?) > > This is, sadly, pretty typical. SMBus devices are often exposed via PCI > even though they're accessed directly via AML. The current behaviour > seems about as good as it gets - we warn the user that this could cause > problems, and they can pass a kernel parameter that allows them to do it > anyway. The proper way to handle it at the BIOS level is to expose the SMBus to the OS by implementing the ACPI SMBus CMI as supported by the i2c-scmi driver. Unfortunately most BIOS do not bother implementing that interface, effectively locking the OS out of the SMBus controller and everything behind it. This has been a major pain for years :( -- Jean Delvare SUSE L3 Support