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

[Hans de Goede <hdegoede@redhat.com>]

Hi Laurent,

On 12/2/21 21:43, Laurent Pinchart wrote:
> Hi Hans,
> 
> Thank you for the patch.
> 
> On Thu, Dec 02, 2021 at 09:13:51PM +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 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
> 
> s/this/that/ (or ". This" ?)

I've gone with ". This" for v2.


> 
>> 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 a 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.
> 
> This will make the life of the Go and Go2 users *much* easier.
> 
>> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>> Cc: Dan Scally <djrscally@gmail.com>
>> Cc: Kate Hsuan <hpa@redhat.com>
>> Cc: Maximilian Luz <luzmaximilian@gmail.com>
>> Signed-off-by: Hans de Goede <hdegoede@redhat.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), },
>> +	{ }
> 
> Reading the commit message, I was going to mention that the match should
> probably be machine-dependent, but that seems to be covered by the PCI
> subsystem ID.
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Thanks you.

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;
>