On 8/17/2023 2:37 PM, Rafael J. Wysocki wrote:
On Thu, Aug 17, 2023 at 9:30 PM Limonciello, Mario
<mario.limonciello@xxxxxxx> wrote:
On 8/17/2023 2:25 PM, Bjorn Helgaas wrote:
On Wed, Aug 16, 2023 at 03:41:43PM -0500, Mario Limonciello wrote:
Since commit 9d26d3a8f1b0 ("PCI: Put PCIe ports into D3 during suspend")
PCIe ports from modern machines (>=2015) are allowed to be put into D3 by
storing a value to the `bridge_d3` variable in the `struct pci_dev`
structure.
...
+static void lpi_check_pci_dev(struct lpi_constraints *entry, struct pci_dev *pdev)
+{
+ pci_power_t target = entry->enabled ? entry->min_dstate : PCI_D0;
+
+ if (pdev->current_state == target)
+ return;
+
+ /* constraint of ACPI D3hot means PCI D3hot _or_ D3cold */
+ if (target == ACPI_STATE_D3_HOT &&
ACPI_STATE_D3_HOT is not a valid pci_power_t value.
Based on this, kernel robot sparse complaints and your comments on v11's
last patch I am going to split off to another function that returns the
pci_power_t state based upon the situation and better comment the reason
for the D0 when not enabled.
+ (pdev->current_state == PCI_D3hot ||
+ pdev->current_state == PCI_D3cold))
+ return;
+
+ if (pm_debug_messages_on)
+ acpi_handle_info(entry->handle,
+ "LPI: PCI device in %s, not in %s\n",
+ acpi_power_state_string(pdev->current_state),
+ acpi_power_state_string(target));
+
+ /* don't try with things that PCI core hasn't touched */
+ if (pdev->current_state == PCI_UNKNOWN) {
+ entry->handle = NULL;
+ return;
+ }
+
+ pci_set_power_state(pdev, target);
It doesn't seem logical for a "check_constraints()" function that
takes no parameters and returns nothing to actively set the PCI power
state.
lpi_check_constraints() returns nothing, and from the fact that it was
previously only called when "pm_debug_messages_on", I infer that it
should have no side effects.
IMHO "lpi_check_constraints" is not a great name because "check"
doesn't suggest anything specific about what it does.
"dump_constraints()" -- fine. "log_unmet_constraints()" -- fine
(seems like the original intention of 726fb6b4f2a8 ("ACPI / PM: Check
low power idle constraints for debug only"), which added it.
Great feedback, thanks. I'm thinking to instead change it to:
lpi_enforce_constraints()
Don't even try to go this way, please.
Originally, the LPI constraints are there to indicate to Windows
whether or not it should attempt to enter Connected/Modern Standby.
Because Linux doesn't do Modern Standby, it doesn't use the LPI
constraints the way Windows does and it really shouldn't do that.
I think that the exercise here is to use the information from the
constraints list as an indication whether or not a given PCI Root Port
is supposed to be put into D3hot/cold on suspend-to-idle and this has
nothing to do with enforcement.
What do you think about me making the changes to pci_prepare_to_sleep()?
Something like this:
@@ -2733,11 +2742,17 @@ int pci_prepare_to_sleep(struct pci_dev *dev)
{
bool wakeup = device_may_wakeup(&dev->dev);
pci_power_t target_state = pci_target_state(dev, wakeup);
+ pci_power_t constraint;
int error;
if (target_state == PCI_POWER_ERROR)
return -EIO;
+ /* if platform indicates device constraint for suspend, use it */
+ constraint = platform_check_constraint(dev, target_state);
+ if (constraint != PCI_POWER_ERROR)
+ target_state = constraint;
+
pci_enable_wake(dev, target_state, wakeup);
error = pci_set_power_state(dev, target_state);
