Re: [PATCH v20 2/2] PCI: Add a quirk for AMD PCIe root ports w/ USB4 controllers

[Mario Limonciello <mario.limonciello@amd.com>]

On 9/30/2023 04:24, Lukas Wunner wrote:
> On Tue, Sep 19, 2023 at 10:27:24PM -0500, Mario Limonciello wrote:
>> --- a/drivers/pci/quirks.c
>> +++ b/drivers/pci/quirks.c
> [...]
>> + * When AMD PCIe root ports with AMD USB4 controllers attached to them are put
>> + * into D3hot or D3cold downstream USB devices may fail to wakeup the system
>> + * from suspend to idle.  This manifests as a missing wakeup interrupt.
>> + *
>> + * Prevent the associated root port from using PME to wake from D3hot or
>> + * D3cold power states during suspend.
>> + * This will effectively put the root port into D0 power state over suspend.
> 
> IIUC, the quirk matches for a Root Port, then searches for a
> USB controller below the Root Port, and if found, searches for the
> Root Port above again to clear or reinstate the PME bits.
> 
> That seems like a roundabout way of doing things.  Have you
> considered matching for the USB controller's Device ID in the quirk,
> then checking whether the Root Port above has the Device ID which
> is known to be broken?
> 

Yeah; this suggestion works.  It's 8 quirks instead of 4, but it's much 
cleaner and easier to follow.  I will send a v21 with this later on.

> Also, since pci_d3cold_enable() / pci_d3cold_disable() are now fixed
> (can no longer be interfered with from user space), you might want to
> consider using them alternatively to clearing PME bits.  They don't
> require access to config space.
> 

I still don't like that userspace can potentially influence state 
selection policy.  Separate from this quirk I'm going to send another 
patch for that.