On Mon, Oct 06, 2025 at 11:32:38AM -0700, Brian Norris wrote:
On Mon, Oct 06, 2025 at 03:52:22PM +0200, Mika Westerberg wrote:
On Fri, Oct 03, 2025 at 03:40:09PM -0700, Brian Norris wrote:
From: Brian Norris briannorris@google.com
When transitioning to D3cold, __pci_set_power_state() will first transition a device to D3hot. If the device was already in D3hot, this will add excess work: (a) read/modify/write PMCSR; and (b) excess delay (pci_dev_d3_sleep()).
How come the device is already in D3hot when __pci_set_power_state() is called? IIRC PCI core will transition the device to low power state so that it passes there the deepest possible state, and at that point the device is still in D0. Then __pci_set_power_state() puts it into D3hot and then turns if the power resource -> D3cold.
What I'm missing here?
Some PCI drivers call pci_set_power_state(..., PCI_D3hot) on their own when preparing for runtime or system suspend, so by the time they hit pci_finish_runtime_suspend(), they're in D3hot. Then, pci_target_state() may still pick a lower state (D3cold).
We might need this change, but maybe this is also an opportunity to remove some of those pci_set_power_state(..., PCI_D3hot) calls from drivers.
I didn't look into any of them in detail, but I would jump at any chance to remove PCI details from driver suspend paths. There are only ~20 calls from suspend functions, ~25 from shutdown, and a few from poweroff. The fact that there are so few makes me think they might be leftovers that could be more fully converted to generic PM.