linux-kernel - Re: [PATCH v9 3/3] PCI/ACPI: Use device constraints to decide PCI target state fallback policy

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Message-ID: <36dfd3cf-37c6-a630-7ef6-376a339a8f8d@amd.com>
Date:   Fri, 4 Aug 2023 10:56:32 -0500
From:   "Limonciello, Mario" <mario.limonciello@....com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     "Rafael J . Wysocki" <rafael@...nel.org>,
        Bjorn Helgaas <helgaas@...nel.org>, 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 v9 3/3] PCI/ACPI: Use device constraints to decide PCI
 target state fallback policy



On 8/4/2023 8:17 AM, Mika Westerberg wrote:
> On Thu, Aug 03, 2023 at 08:02:29PM -0500, Mario Limonciello wrote:
>> +/**
>> + * acpi_pci_device_constraint - determine if the platform has a contraint for the device
>> + * @dev: PCI device to check
>> + * @result (out): the constraint specified by the platform
>> + *
>> + * If the platform has specified a constraint for a device, this function will
>> + * return 0 and set @result to the constraint.
>> + * Otherwise, it will return an error code.
>> + */
>> +int acpi_pci_device_constraint(struct pci_dev *dev, int *result)
>> +{
>> +	int constraint;
>> +
>> +	constraint = acpi_get_lps0_constraint(&dev->dev);
>> +	pci_dbg(dev, "ACPI device constraint: %d\n", constraint);
>> +	if (constraint < 0)
>> +		return constraint;
>> +	*result = constraint;
> 
> Is there something preventing to return the constraint directly instead
> of storing it into "result"?

My aim was to make the caller use it a pass/fail function.

I'll adjust it so that the caller would look for >= 0 instead.

> 
>> +
>> +	return 0;
>> +}
>> +
>>   static void acpi_pci_config_space_access(struct pci_dev *dev, bool enable)
>>   {
>>   	int val = enable ? ACPI_REG_CONNECT : ACPI_REG_DISCONNECT;
>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>> index 60230da957e0c..6c70f921467c6 100644
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -1082,6 +1082,14 @@ static inline bool platform_pci_bridge_d3(struct pci_dev *dev)
>>   	return acpi_pci_bridge_d3(dev);
>>   }
>>   
>> +static inline int platform_get_constraint(struct pci_dev *dev, int *result)
> 
> Ditto here.
> 
>> +{
>> +	if (pci_use_mid_pm())
>> +		return -ENODEV;
>> +
>> +	return acpi_pci_device_constraint(dev, result);
>> +}
>> +