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 patche 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..468c0733838e 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 + * + * 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. + * + * The UUID of the _DSM control method, together with other information like + * which delay values can be optimized, etc. is defined in a ECN available on + * PCIsig.com titled as: ACPI additions for FW latency optimizations. + * Function 9 of the ACPI _DSM control method, if available 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 available 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; -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
