Commit e6b14206 authored by Hans de Goede's avatar Hans de Goede Committed by Lee Jones
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mfd: intel-lpss: Fix I2C4 not being available on the Microsoft Surface Go & Go 2

Many DSDTs for Kaby Lake and Kaby Lake Refresh models contain a
_SB.PCI0.GEXP ACPI Device node describing an I2C attached PCA953x
GPIO expander.

This seems to be something which is copy and pasted from the DSDT
from some reference design since this ACPI Device is present even on
models where no such GPIO expander is used at all, such as on the
Microsoft Surface Go & Go 2.

This ACPI Device is a problem because it contains a SystemMemory
OperationRegion which covers the MMIO for the I2C4 I2C controller. This
causes the MFD cell for the I2C4 controller to not be instantiated due
to a resource conflict, requiring the use of acpi_enforce_resources=lax
to work around this.

I have done an extensive analysis of all the ACPI tables on the
Microsoft Surface Go and the _SB.PCI0.GEXP ACPI Device's methods are
not used by any code in the ACPI tables, neither are any of them
directly called by any Linux kernel code. This is unsurprising...
parent ad4ddfac
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