Re: [Intel-gfx] [PATCH] i2c: i801: Allow ACPI SystemIO OpRegion to conflict harder

[David Weinehall]

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