On Mon, Jun 26, 2017 at 04:40:08PM -0400, Lyude wrote: > There's quite a number of machines on the market, mainly Lenovo > ThinkPads, that make the horrible mistake in their firmware of reusing > the PCIBAR space reserved for the SMBus for things that are completely > unrelated to the SMBus controller, such as the OpRegion used for i915. > This is very bad and entirely evil, but with Lenovo's historically poor > track record of fixing their firmware, it is extremely unlikely this is > ever going to be properly fixed. > > So, while it would be nice if we could just cut off the SMBus controller > and call it a day this unfortunately breaks RMI4 mode completely for > most of the ThinkPads. Even though this behavior is extremely wrong, for > whatever reason sharing the PCIBAR between the OpRegion and SMBus seems > to be just fine. Regardless however, I think it's safe to assume that > when the BIOS accesses the PCIBAR space of the SMBus controller like > this that it's trying to get to something else that we mapped the SMBus > controller over. > > On my X1 Carbon, this assumption appears to be correct. I've traced down > the firmware accesses to being caused by the firmware mistakenly placing > the SWSCI mailbox for i915 on top of the SMBus host controller region. > And indeed, blacklisting i915 causes the firmware to never attempt to > touch this region. > > So, in order to try to workaround this and not break either SMBus or > i915, we temporarily unmap the PCI device for the SMBus controller, > do the thing that the firmware wanted to do, then remap the device and > report a firmware bug. > > Signed-off-by: Lyude <lyude@xxxxxxxxxx> > Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > Cc: Benjamin Tissoires <btissoir@xxxxxxxxxx> > Cc: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> > Cc: Jean Delvare <jdelvare@xxxxxxx> > Cc: Wolfram Sang <wsa@xxxxxxxxxxxxx> > Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx > --- > So: unfortunately > > a7ae81952cda (i2c: i801: Allow ACPI SystemIO OpRegion to conflict with PCI BAR) > > Seems to prevent the ThinkPad X1 Carbon 4th gen and the T460s from actually > using their SMBus controllers at all. As mentioned above, I've traced the issue > down to the firmware responding to the SWSCI by sticking data in places it > shouldn't, e.g. the SMBus registers. > > I'm entirely unsure if this patch is the correct fix for this, and wouldn't be > at all surprised if it's just as bad of a patch as I think it is ;P. So I > figured I'd send it to intel-gfx and the authors of the original version of this > patch to get their take on it and see if there might be something less hacky we > can do to fix this. How does "that other" operating system handle this? FWIW I own a ThinkPad X1 Carbon 4th Gen, so I'm happy for your work on it :) Kind regards, David
