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

[Bjorn Helgaas <helgaas@kernel.org>]

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.

> +	    (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.

> +}
> +
>  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
>