Re: [PATCH] PCI / ACPI: PCI delay optimization from ACPI

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On 03/09/2015 10:33 PM, Rafael J. Wysocki wrote:
> On Monday, March 09, 2015 03:46:01 PM Aaron Lu wrote:
>> An ECN meant to specify possible delay optimizations is available on
>> the PCI website:
>> https://www.pcisig.com/specifications/conventional/pci_firmware/ECN_fw_latency_optimization_final.pdf
>> where it has defined two functions for an UUID specified _DSM:
>> Function 8: If system firmware assumes the responsibility of post
>> Conventional Reset delay (and informs the Operating System via this DSM
>> function) on Sx Resume (such as boot from ACPI S5, or resume from ACPI
>> S4 or S3 states), the Operating System may assume sufficient time has
>> elapsed since the end of reset, and devices within the PCI subsystem are
>> ready for Configuration Access.
>> If the system firmware supports runtime power gating on any of the
>> device within PCI subsystem covered by this DSM function, the system
>> firmware is responsible for covering the necessary post power-on reset
>> delay.
>>
>> Function 9: Specify various smaller delay values than required by the
>> SPEC for individual PCI devices like shorter delay values after
>> conventional reset, D3hot to D0 transition, functional level reset, etc.
>>
>> This patch adds support for function 8 and part of function 9. For
>> function 8, the patch will check if the required _DSM function satisfies
>> the requirement and then set the per PCI device's d3cold_delay variable
>> to zero. For function 9, the values affecting delays after conventional
>> reset and D3hot->D0 are examined and the per PCI device's d3cold_delay
>> and d3_delay are updated if the _DSM's return value is smaller than what
>> the SPEC requires.
>>
>> Signed-off-by: Aaron Lu <aaron.lu@xxxxxxxxx>
>> ---
>>  drivers/pci/pci-acpi.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 61 insertions(+)
>>
>> diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
>> index 489063987325..c833b054c00c 100644
>> --- a/drivers/pci/pci-acpi.c
>> +++ b/drivers/pci/pci-acpi.c
>> @@ -558,6 +558,64 @@ static struct acpi_device *acpi_pci_find_companion(struct device *dev)
>>  				      check_children);
>>  }
>>  
>> +/**
>> + * pci_acpi_delay_optimize - optimize PCI D3 and D3cold delay from ACPI
>> + * @pdev: the PCI device whose delay is to be updated
>> + * @adev: the companion ACPI device of this PCI device
>> + *
>> + * Description:
> 
> The word "Description" above is not necessary.
> 
>> + *   This function is used to update the d3_delay and d3cold_delay of a PCI
> 
> I'd simply say
> 
> "Update the d3_delay and d3cold_delay of a PCI device from the ACPI _DSM control
> method of either its own or its parent bridge."
> 
> I'd add an empty line here and then the rest of the below starting with "The UUID ...".

OK.

> 
>> + *   device from ACPI _DSM control method of either its own or its parent
>> + *   bridge device. The UUID of the _DSM control method, together with other
>> + *   information like which delay values can be optimized, etc. is defined in
>> + *   the fw_latency_optimization ECN availabe on PCIsig.com.
> 
> The ECN has a number or title I suppose?

Yes.

Thanks for the review and suggestion, I'll send an updated one.

Regards,
Aaron

> 
>> + *   Function 9 of the ACPI _DSM control method, if availabe for a specific PCI
>> + *   device, provides various possible delay values that are less than what the
>> + *   SPEC requires. Here, we only deal with d3_delay and d3cold_delay. Others
>> + *   can be added later.
>> + *   Function 8 of the ACPI _DSM control method, if availabe for a specific PCI
>> + *   bridge, means all its children devices do not need the reset delay when
>> + *   leaving from D3cold state.
>> + */
>> +static void pci_acpi_delay_optimize(struct pci_dev *pdev, struct acpi_device *adev)
>> +{
>> +	const u8 uuid[] = {
>> +		0xd0, 0x37, 0xc9, 0xe5, 0x53, 0x35, 0x7a, 0x4d,
>> +		0x91, 0x17, 0xea, 0x4d, 0x19, 0xc3, 0x43, 0x4d
>> +	};
>> +	int revision = 3, function = 9, value;
>> +	acpi_handle handle = adev->handle;
>> +	union acpi_object *obj, *elements;
>> +
>> +	obj = acpi_evaluate_dsm(handle, uuid, revision, function, NULL);
>> +	if (obj) {
>> +		if (obj->type == ACPI_TYPE_PACKAGE && obj->package.count == 5) {
>> +			elements = obj->package.elements;
>> +			if (elements[3].type == ACPI_TYPE_INTEGER) {
>> +				value = (int)elements[3].integer.value / 1000;
>> +				if (value < PCI_PM_D3_WAIT)
>> +					pdev->d3_delay = value;
>> +			}
>> +			if (elements[0].type == ACPI_TYPE_INTEGER) {
>> +				value = (int)elements[0].integer.value / 1000;
>> +				if (value < PCI_PM_D3COLD_WAIT)
>> +					pdev->d3cold_delay = value;
>> +			}
>> +		}
>> +		kfree(obj);
>> +	}
>> +
>> +	function = 8;
>> +	handle = ACPI_HANDLE(pdev->bus->bridge);
>> +	obj = acpi_evaluate_dsm(handle, uuid, revision, function, NULL);
>> +	if (!obj)
>> +		return;
>> +
>> +	if (obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 1)
>> +		pdev->d3cold_delay = 0;
>> +	kfree(obj);
>> +}
>> +
>>  static void pci_acpi_setup(struct device *dev)
>>  {
>>  	struct pci_dev *pci_dev = to_pci_dev(dev);
>> @@ -566,6 +624,9 @@ static void pci_acpi_setup(struct device *dev)
>>  	if (!adev)
>>  		return;
>>  
>> +	if (pci_dev->pm_cap)
>> +		pci_acpi_delay_optimize(pci_dev, adev);
>> +
>>  	pci_acpi_add_pm_notifier(adev, pci_dev);
>>  	if (!adev->wakeup.flags.valid)
>>  		return;
>>
> 

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