From mboxrd@z Thu Jan 1 00:00:00 1970 From: Prarit Bhargava Subject: Re: Haswell systems & i801 i2c driver Date: Wed, 09 Apr 2014 12:21:40 -0400 Message-ID: <53457394.1020404@redhat.com> References: <5342E7C0.4050209@redhat.com> <1396902638.5276.2.camel@x230> <20140407225620.23d52a0c@endymion.delvare> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140407225620.23d52a0c-R0o5gVi9kd7kN2dkZ6Wm7A@public.gmane.org> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Jean Delvare Cc: Matthew Garrett , 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, 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 04/07/2014 04:56 PM, Jean Delvare wrote: > 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 :( Hey Jean, Thanks for the info. I'm about to RFC an algorithm patch for the i801 ACPI SBUS. I dunno if it is really a good thing to do outside of Intel or if we should wait for a CMI. OTOH it seems to work and your comment that "This has been a major pain for years" worries me that we'll never see a solution. P. >