Re: [PATCH v2] mfd: intel-lpss: Fix I2C4 not being available on the Microsoft Surface Go & Go 2

[Mika Westerberg]

On Fri, Dec 03, 2021 at 12:51:08PM +0100, Hans de Goede wrote:
> 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 since
> running i2cdetect on the I2C4 bus shows that there is no GPIO
> expander chip present on these devices at all.
> 
> This commit adds a PCI subsystem vendor:device table listing PCI devices
> where it is known to be safe to ignore resource conflicts with ACPI
> declared SystemMemory regions.
> 
> This makes the I2C4 bus work out of the box on the Microsoft Surface
> Go & Go 2, which is necessary for the cameras on these devices to work.
> 
> Cc: Dan Scally <djrscally@xxxxxxxxx>
> Cc: Kate Hsuan <hpa@xxxxxxxxxx>
> Cc: Maximilian Luz <luzmaximilian@xxxxxxxxx>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
> Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>

Acked-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>