linux-kernel - Re: [PATCH 2/2] xhci: pci: Put XHCI controllers into D3hot at shutdown

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Message-ID: <bd380d71-4ebe-4889-9ed8-aeefec2b2b0e@linux.intel.com>
Date: Wed, 28 Aug 2024 17:02:10 +0300
From: Mathias Nyman <mathias.nyman@...ux.intel.com>
To: Peter Chen <peter.chen@...nel.org>,
 Mario Limonciello <mario.limonciello@....com>
Cc: superm1@...nel.org, Mathias Nyman <mathias.nyman@...el.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "open list:USB XHCI DRIVER" <linux-usb@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>,
 Kai-Heng Feng <kai.heng.feng@...onical.com>,
 mika.westerberg@...ux.intel.com, stern@...land.harvard.edu
Subject: Re: [PATCH 2/2] xhci: pci: Put XHCI controllers into D3hot at
 shutdown

>>> Hi Mario & Mathias,
>>>
>>> According to xHCI spec v1.2: A.1.2 Power State Definitions:
>>>
>>> 	Software shall place each downstream USB port with power
>>> 	enabled into the Suspend or Disabled state before it
>>> 	attempts to move the xHC out of the D0 power state.
>>>
>>> But I have not found any USB core code does it, do you have any ideas
>>> about it?
>>>
>>> We have added the similar codes at non-PCI USB platform, but met above
>>> concerns. In fact, we met kernel dump that the thread usb-storage try
>>> to access the port status when the platform xHCI code has already put
>>> the controller to D3.
>>>
>>> Best regards,
>>> Peter
>>>
>>>
>>
>> This is pretty tangential to my patch.  But FWIW in case you missed we're
>> going to discard this patch in favor of another approach in PCI core.
>>
>> Regarding your point though If I'm not mistaken this should be handled by
>> the Linux parent/child device model.  Each of the ports should be children
>> of the hub they're connected to and the hub a child of the controller.  So
>> when doing any actions that start runtime PM on the host controller the
>> children need to first be in runtime PM.
>>
> 
> It seems there is no runtime PM suspend for xhci and USB core at
> .shutdown currently. Alan & Mathias, please correct me if I was wrong.
> 

I think you are right.  At shutdown we only halt the xHC.
We don't force ports to suspend or disable state.
We only put some selected xHC to D3

USB 2 ports might suspend themselves if there is no activity.

Doesn't seem like usb core hcd code, or hub driver does anything either.

Thanks
Mathias