Hi, This series adds support for notifying the PCI drivers like NVMe about the transition of PCI devices into powerdown mode during system suspend. Background ---------- On Qcom SC7280 based Chrome platforms, the RPMh will turn off the power to all PCIe devices during system suspend for aggressive powersaving. Currently, there is no way for the PCI device drivers to learn about this situation. Some of the drivers assume that the power will be retained and some others assume that the power may be taken down. We faced the issue with NVMe PCI driver, where the driver expects the NVMe device to be in APST (Autonomous Power State Transition) state for power saving during system suspend. So when the power goes down, the NVMe driver fails to bringup the device during resume. Previous work ------------- We tried to fix this issue in a couple of ways: 1. The NVMe PCI driver checks for the existence of "StorageD3Enable" ACPI property in the suspend path. If the property is found, the driver assumes that the device may go to poweroff state and shutdowns the device accordingly. As like the ACPI based systems, we also tried to get the support in place for DT based systems. But that didn't get accepted: https://lore.kernel.org/all/Yl+6V3pWuyRYuVV8@xxxxxxxxxxxxx/T/ 2. Keith Busch proposed a module params based approach. The parameter when set, will allow the driver to support APST during suspend. Absence of that parameter will let the driver shutdown the device. This also did not get accepted: https://lore.kernel.org/linux-nvme/20220201165006.3074615-1-kbusch@xxxxxxxxxx/ Proposal -------- Christoph suggested to add a notification in the PCI/PM core to let the NVMe driver know that the device will go into powerdown state during suspend. https://lore.kernel.org/all/Yg0wklcJ3ed76Jbk@xxxxxxxxxxxxx/ Hence in this series, a "suspend_poweroff" flag is introduced in the host bridge struct. When this flag is set by the PCI RC drivers, the PCI device driver like NVMe can shutdown the device during suspend. In the coming days, the usage of this flag could be extended to other PCI drivers as well. In this series, the system suspend/resume support is also added to the Qcom PCIe RC driver for SC7280. During the suspend time, the RC driver will put the device into D3cold and recover it during resume. So even though RPMh is cutting off the power to PCIe domain, it is necessary to put the device in D3cold by the PCIe RC driver for proper working. Testing ------- This series has been tested on SC7280 IDP board connected to a NVMe PCI device. Thanks, Mani Manivannan Sadhasivam (2): PCI: Add a flag to notify PCI drivers about powerdown during suspend nvme-pci: Make use of "suspend_poweroff" flag during system suspend Prasad Malisetty (1): PCI: qcom: Add system PM support drivers/nvme/host/pci.c | 3 +- drivers/pci/controller/dwc/pcie-qcom.c | 108 +++++++++++++++++++++++++ include/linux/pci.h | 2 + 3 files changed, 112 insertions(+), 1 deletion(-) -- 2.25.1
