Re: Haswell systems & i801 i2c driver

[Prarit Bhargava <prarit-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.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.
>