From: Brian Norris Date: Fri, 3 Oct 2025 22:40:09 +0000 (-0700) Subject: PCI/PM: Avoid redundant delays on D3hot->D3cold X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4d982084507d663df160546c4c48066a8887ed89;p=thirdparty%2Fkernel%2Flinux.git PCI/PM: Avoid redundant delays on D3hot->D3cold When transitioning to D3cold, __pci_set_power_state() first transitions to D3hot. If the device was already in D3hot, this adds excess work: (a) read/modify/write PMCSR; and (b) excess delay (pci_dev_d3_sleep()). For (b), we already performed the necessary delay on the previous D3hot entry; this was extra noticeable when evaluating runtime PM transition latency. Check whether we're already in the target state before continuing. Note that __pci_set_power_state() already does this same check for other state transitions, but D3cold is special because __pci_set_power_state() converts it to D3hot for the purposes of PMCSR. This seems to be an oversight in commit 0aacdc957401 ("PCI/PM: Clean up pci_set_low_power_state()"). Fixes: 0aacdc957401 ("PCI/PM: Clean up pci_set_low_power_state()") Signed-off-by: Brian Norris Signed-off-by: Brian Norris [bhelgaas: reverse test to match other "dev->current_state == state" cases] Signed-off-by: Bjorn Helgaas Link: https://patch.msgid.link/20251003154008.1.I7a21c240b30062c66471329567a96dceb6274358@changeid --- diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index 13dbb405dc31f..86ccbd0efb495 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -1488,6 +1488,9 @@ static int pci_set_low_power_state(struct pci_dev *dev, pci_power_t state, bool || (state == PCI_D2 && !dev->d2_support)) return -EIO; + if (dev->current_state == state) + return 0; + pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr); if (PCI_POSSIBLE_ERROR(pmcsr)) { pci_err(dev, "Unable to change power state from %s to %s, device inaccessible\n",