Re: [PATCH v12 9/9] ACPI: x86: s2idle: Enforce LPS0 constraints for PCI devices

[Limonciello, Mario]

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()

> > +}
> > +
> >   static void lpi_check_constraints(void)
> >   {
> >   	struct lpi_constraints *entry;
> >   
> >   	for_each_lpi_constraint(entry) {
> >   		struct acpi_device *adev = acpi_fetch_acpi_dev(entry->handle);
> > +		struct device *dev;
> >   
> >   		if (!adev)
> >   			continue;
> >   
> > +		/* Check and adjust PCI devices explicitly */
> > +		dev = acpi_get_first_physical_node(adev);
> > +		if (dev && dev_is_pci(dev)) {
> > +			lpi_check_pci_dev(entry, to_pci_dev(dev));
> > +			continue;
> > +		}
> > +		if (!entry->enabled)
> > +			continue;
> >   		acpi_handle_debug(entry->handle,
> >   			"LPI: required min power state:%s current power state:%s\n",
> >   			acpi_power_state_string(entry->min_dstate),
> >   			acpi_power_state_string(adev->power.state));
> >   
> > -		if (!adev->flags.power_manageable) {
> > -			acpi_handle_info(entry->handle, "LPI: Device not power manageable\n");
> > -			entry->handle = NULL;
> > -			continue;
> > -		}
> > -
> > -		if (adev->power.state < entry->min_dstate)
> > +		if (pm_debug_messages_on &&
> > +		    adev->flags.power_manageable &&
> > +		    adev->power.state < entry->min_dstate)
> >   			acpi_handle_info(entry->handle,
> >   				"LPI: Constraint not met; min power state:%s current power state:%s\n",
> >   				acpi_power_state_string(entry->min_dstate),
> > @@ -512,8 +546,7 @@ int acpi_s2idle_prepare_late(void)
> >   	if (!lps0_device_handle || sleep_no_lps0)
> >   		return 0;
> >   
> > -	if (pm_debug_messages_on)
> > -		lpi_check_constraints();
> > +	lpi_check_constraints();
> >   
> >   	/* Screen off */
> >   	if (lps0_dsm_func_mask > 0)
> > --
> > 2.34.1