Date:   Wed, 29 Dec 2021 13:17:31 +0000
From:   Lee Jones <lee.jones@linaro.org>
To:     Hans de Goede <hdegoede@redhat.com>
Cc:     Andy Shevchenko <andy@infradead.org>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        linux-kernel@vger.kernel.org, Dan Scally <djrscally@gmail.com>,
        Kate Hsuan <hpa@redhat.com>,
        Maximilian Luz <luzmaximilian@gmail.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Andy Shevchenko <andy.shevchenko@gmail.com>
Subject: Re: [PATCH v2] mfd: intel-lpss: Fix I2C4 not being available on the
 Microsoft Surface Go & Go 2
Message-ID: <Ycxf6/UulLysJ8HA@google.com>
References: <20211203115108.89661-1-hdegoede@redhat.com>
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On Fri, 03 Dec 2021, 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@gmail.com>
> Cc: Kate Hsuan <hpa@redhat.com>
> Cc: Maximilian Luz <luzmaximilian@gmail.com>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> ---
> Changes in v2:
> - Use PCI_VENDOR_ID_INTEL instead of 0x8086
> - Small tweaks to commit message
> - Added Laurent's and Andy's Reviewed-by
> ---
>  drivers/mfd/intel-lpss-pci.c | 12 ++++++++++++
>  drivers/mfd/intel-lpss.c     |  1 +
>  drivers/mfd/intel-lpss.h     |  1 +
>  3 files changed, 14 insertions(+)

Applied, thanks.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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