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

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Message-ID: <a2d551d3-7426-1dff-9936-d4bde10c4a59@redhat.com>
Date:   Fri, 3 Dec 2021 12:32:35 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Andy Shevchenko <andy@...radead.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Dan Scally <djrscally@...il.com>, Kate Hsuan <hpa@...hat.com>,
        Maximilian Luz <luzmaximilian@...il.com>
Subject: Re: [PATCH] mfd: intel-lpss: Fix I2C4 not being available on the
 Microsoft Surface Go & Go 2

Hi,

On 12/2/21 22:15, Andy Shevchenko wrote:
> On Thu, Dec 2, 2021 at 10:14 PM Hans de Goede <hdegoede@...hat.com> wrote:
>>
>> Many DSDTs for Kaby Lake and Kaby Lake Refresh models contain a
>> _SB.PCI0.GEXP ACPI Device node describing an I2C attached GPIO expander.
> 
> For the record (and probably good to mention it's here) it's a PCA953x
> compatible one.

Ack, added to the commit msg for v2.

>> 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.
> 
> Does this come from schematics? Or..? Ah, I see below.
> 
>> 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.
> 
> Right.
> 
>> 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.
> 
> I believe it's an optional component on our reference designs (I saw a
> lot of those expanders on our development boards).
> 
>> This commit adds a PCI subsystem vendor:device table listing PCI devices
>> where it is known to be safe to ignore a resource-conflicts with ACPI
> 
> ignore resource conflicts

Ack, fixed for v2.


> (no article, no dash) ?
> 
>> 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.
> 
> After addressing comments
> Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
> Thanks for the patch!
> 
>> Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>
>> Cc: Dan Scally <djrscally@...il.com>
>> Cc: Kate Hsuan <hpa@...hat.com>
>> Cc: Maximilian Luz <luzmaximilian@...il.com>
>> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
>> ---
>>  drivers/mfd/intel-lpss-pci.c | 12 ++++++++++++
>>  drivers/mfd/intel-lpss.c     |  1 +
>>  drivers/mfd/intel-lpss.h     |  1 +
>>  3 files changed, 14 insertions(+)
>>
>> diff --git a/drivers/mfd/intel-lpss-pci.c b/drivers/mfd/intel-lpss-pci.c
>> index a872b4485eac..593290ff08a6 100644
>> --- a/drivers/mfd/intel-lpss-pci.c
>> +++ b/drivers/mfd/intel-lpss-pci.c
>> @@ -17,6 +17,15 @@
>>
>>  #include "intel-lpss.h"
>>
>> +/* Some DSDTs have an unused GEXP ACPI device conflicting with I2C4 resources */
>> +static const struct pci_device_id ignore_resource_conflicts_ids[] = {
>> +       /* Microsoft Surface Go (version 1) I2C4 */
>> +       { PCI_DEVICE_SUB(0x8086, 0x9d64, 0x152d, 0x1182), },
>> +       /* Microsoft Surface Go 2 I2C4 */
>> +       { PCI_DEVICE_SUB(0x8086, 0x9d64, 0x152d, 0x1237), },
> 
> Can we use PCI_VENDOR_ID_INTEL?

Done for v2.

Thank you for the review.

Regards,

Hans

> 
>> +       { }
>> +};
>> +
>>  static int intel_lpss_pci_probe(struct pci_dev *pdev,
>>                                 const struct pci_device_id *id)
>>  {
>> @@ -35,6 +44,9 @@ static int intel_lpss_pci_probe(struct pci_dev *pdev,
>>         info->mem = &pdev->resource[0];
>>         info->irq = pdev->irq;
>>
>> +       if (pci_match_id(ignore_resource_conflicts_ids, pdev))
>> +               info->ignore_resource_conflicts = true;
>> +
>>         pdev->d3cold_delay = 0;
>>
>>         /* Probably it is enough to set this for iDMA capable devices only */
>> diff --git a/drivers/mfd/intel-lpss.c b/drivers/mfd/intel-lpss.c
>> index 0e15afc39f54..cfbee2cfba6b 100644
>> --- a/drivers/mfd/intel-lpss.c
>> +++ b/drivers/mfd/intel-lpss.c
>> @@ -401,6 +401,7 @@ int intel_lpss_probe(struct device *dev,
>>                 return ret;
>>
>>         lpss->cell->swnode = info->swnode;
>> +       lpss->cell->ignore_resource_conflicts = info->ignore_resource_conflicts;
>>
>>         intel_lpss_init_dev(lpss);
>>
>> diff --git a/drivers/mfd/intel-lpss.h b/drivers/mfd/intel-lpss.h
>> index 22dbc4aed793..062ce95b68b9 100644
>> --- a/drivers/mfd/intel-lpss.h
>> +++ b/drivers/mfd/intel-lpss.h
>> @@ -19,6 +19,7 @@ struct software_node;
>>
>>  struct intel_lpss_platform_info {
>>         struct resource *mem;
>> +       bool ignore_resource_conflicts;
>>         int irq;
>>         unsigned long clk_rate;
>>         const char *clk_con_id;
>> --
>> 2.33.1
>>
> 
>