linux-kernel - Re: [PATCH v5 2/2] PCI: Don't assume root ports are power manageable

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Message-ID: <5c6d4fc9-943b-ecc1-b457-e24451ab2e29@amd.com>
Date:   Wed, 7 Jun 2023 15:36:52 -0500
From:   "Limonciello, Mario" <mario.limonciello@....com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        S-k Shyam-sundar <Shyam-sundar.S-k@....com>,
        Natikar Basavaraj <Basavaraj.Natikar@....com>,
        Deucher Alexander <Alexander.Deucher@....com>,
        "Rafael J . Wysocki" <rafael@...nel.org>, linux-pm@...r.kernel.org,
        Iain Lane <iain@...ngesquash.org.uk>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [PATCH v5 2/2] PCI: Don't assume root ports are power manageable


On 6/7/2023 3:01 AM, Lukas Wunner wrote:
> On Tue, May 30, 2023 at 11:39:47AM -0500, Mario Limonciello wrote:
>> +	/*
>> +	 * It's not safe to put root ports that don't support power
>> +	 * management into D3.
>> +	 */
>> +	if (pci_pcie_type(bridge) == PCI_EXP_TYPE_ROOT_PORT &&
>> +	    !platform_pci_power_manageable(bridge))
>> +		return false;
>> +
>>   	/*
>>   	 * It should be safe to put PCIe ports from 2015 or newer
>>   	 * to D3.
> My recollection is that we began suspending Root Ports to D3hot because
> otherwise low power states of the whole CPU package could not be reached
> on certain Intel CPUs from the 2015+ era.
>
> Do we know if the DSDT of all those systems contains the required ACPI
> objects to continue runtime suspending their Root Ports after this change?
> Otherwise these systems would experience a power regression.
>
> Thanks,
>
> Lukas
You might not have been CC'ed on my earlier patches, but
I was worried about a similar problem and at least in one
of the earlier versions was adjusting the existing
heuristic of ">= 2015" to "Intel & >= 2015".

That being said, this most recent version got R-b and A-b
tags from 3 Intel guys, I would think they cross
referenced reference systems to make that assertion before
adding tags.