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Subject: Re: Time to re-enable Runtime PM per default for PCI devcies?
To:     Lukas Wunner <lukas@wunner.de>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Bjorn Helgaas <helgaas@kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Kai Heng Feng <kai.heng.feng@canonical.com>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <79940973-b631-90f9-dbc4-9579c6000816@gmail.com>
 <20201117163817.GA1397220@bjorn-Precision-5520>
 <CAJZ5v0ipMJ1gCB7okpROG_yAUi5Q8LknqeH+Jpdrjbb4D_vfuQ@mail.gmail.com>
 <9ca0fb46-9e65-31e2-103f-1c98ce8362c7@gmail.com>
 <20201231040735.GA2075@wunner.de>
From:   Heiner Kallweit <hkallweit1@gmail.com>
Message-ID: <4eb10092-e3f9-c9be-2dec-e6de8aeedf97@gmail.com>
Date:   Thu, 31 Dec 2020 10:38:12 +0100
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On 31.12.2020 05:07, Lukas Wunner wrote:
> On Wed, Dec 30, 2020 at 11:56:04PM +0100, Heiner Kallweit wrote:
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -3024,7 +3024,9 @@ void pci_pm_init(struct pci_dev *dev)
>>  	u16 status;
>>  	u16 pmc;
>>  
>> -	pm_runtime_forbid(&dev->dev);
>> +	if (pci_acpi_forbid_runtime_pm())
>> +		pm_runtime_forbid(&dev->dev);
>> +
> 
> Generic PCI code usually does not call ACPI-specific functions directly,
> but rather through a pci_platform_pm_ops callback.
> 
> FWIW, if platform_pci_power_manageable() returns true, it can probably
> be assumed that allowing runtime PM by default is okay.  So as a first
> step, you may want to call that instead of adding a new callback.
> 
I don't think that's sufficient. Most likely all the broken old systems
return true for platform_pci_power_manageable(). So yes, most likely
we'd need a new callback if we want to have the platform ops abstraction.
But it could be an optional callback, something like: forbid_runtime_pm
The question is just: is it worth it?

By the way: pci_set_platform_pm() returns an error if a callback isn't
set, but no existing caller bothers to check the return code.

> Thanks,
> 
> Lukas
> 
Heiner