Re: [PATCH] [RFC] PCI/PM: Do not RPM suspend devices without drivers

["Wysocki, Rafael J" <rafael.j.wysocki@intel.com>]

On 10/26/2024 2:19 AM, Marek Vasut wrote:
> On 10/13/24 1:03 PM, Lukas Wunner wrote:
>> On Sat, Oct 12, 2024 at 02:48:48AM +0200, Marek Vasut wrote:
>>> The pci_host_probe() does reallocate BARs for devices which start up 
>>> with
>>> uninitialized BAR addresses set to 0 by calling 
>>> pci_bus_assign_resources(),
>>> which updates the device config space content.
>>>
>>> At the same time, pci_pm_runtime_suspend() triggers pci_save_state() 
>>> for
>>> all devices which do not have drivers assigned to them to store current
>>> content of their config space registers.

What exactly do you mean by "at the same time"?


>> [...]
>>> Work around the issue by not suspending pci_bus_type devices which do
>>> not have driver assigned to them, keep those devices active to prevent
>>> pci_save_state() from being called. Once a proper driver takes over, it
>>> can RPM manage the device correctly.
>>
>> It sounds like you may want to acquire a runtime PM reference
>> or disable runtime PM for the duration of the bus scan (or at
>> least device scan) rather than the proposed workaround.
> I was hoping to get at least an confirmation that this issue really 
> exists and that I'm not chasing some nonsense. Thoughts ?