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

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Message-ID: <bb7bba27-ddb2-4c64-8a6b-3ce4e635320e@rowland.harvard.edu>
Date: Wed, 28 Aug 2024 10:09:05 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc: Peter Chen <peter.chen@...nel.org>,
	Mario Limonciello <mario.limonciello@....com>, 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
Subject: Re: [PATCH 2/2] xhci: pci: Put XHCI controllers into D3hot at
 shutdown

On Wed, Aug 28, 2024 at 05:02:10PM +0300, Mathias Nyman wrote:
> > > > 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.

That's right.  Host controller drivers are supposed to handle shutdown 
operations by themselves.  The USB core doesn't do anything.

Alan Stern