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

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Message-ID: <beb88d67-9437-4d7a-b1b0-a763583df17e@amd.com>
Date:   Thu, 17 Aug 2023 14:30:02 -0500
From:   "Limonciello, Mario" <mario.limonciello@....com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     "Rafael J . Wysocki" <rafael@...nel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-acpi@...r.kernel.org,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Iain Lane <iain@...ngesquash.org.uk>,
        Shyam-sundar S-k <Shyam-sundar.S-k@....com>
Subject: Re: [PATCH v12 9/9] ACPI: x86: s2idle: Enforce LPS0 constraints for
 PCI devices



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
>>