Re: [PATCH] xhci: Fix perceived dead host due to runtime suspend race with event handler

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Jul 19, 2018 at 12:23:22AM +0800, Kai-Heng Feng wrote:
> From: Mathias Nyman <mathias.nyman@linux.intel.com>
> 
> commit 229bc19fd7aca4f37964af06e3583c1c8f36b5d6 upstream.
> 
> Don't rely on event interrupt (EINT) bit alone to detect pending port
> change in resume. If no change event is detected the host may be suspended
> again, oterwise roothubs are resumed.
> 
> There is a lag in xHC setting EINT. If we don't notice the pending change
> in resume, and the controller is runtime suspeded again, it causes the
> event handler to assume host is dead as it will fail to read xHC registers
> once PCI puts the controller to D3 state.
> 
> [  268.520969] xhci_hcd: xhci_resume: starting port polling.
> [  268.520985] xhci_hcd: xhci_hub_status_data: stopping port polling.
> [  268.521030] xhci_hcd: xhci_suspend: stopping port polling.
> [  268.521040] xhci_hcd: // Setting command ring address to 0x349bd001
> [  268.521139] xhci_hcd: Port Status Change Event for port 3
> [  268.521149] xhci_hcd: resume root hub
> [  268.521163] xhci_hcd: port resume event for port 3
> [  268.521168] xhci_hcd: xHC is not running.
> [  268.521174] xhci_hcd: handle_port_status: starting port polling.
> [  268.596322] xhci_hcd: xhci_hc_died: xHCI host controller not responding, assume dead
> 
> The EINT lag is described in a additional note in xhci specs 4.19.2:
> 
> "Due to internal xHC scheduling and system delays, there will be a lag
> between a change bit being set and the Port Status Change Event that it
> generated being written to the Event Ring. If SW reads the PORTSC and
> sees a change bit set, there is no guarantee that the corresponding Port
> Status Change Event has already been written into the Event Ring."
> 
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
> ---
>  drivers/usb/host/xhci.c | 40 +++++++++++++++++++++++++++++++++++++---
>  drivers/usb/host/xhci.h |  4 ++++
>  2 files changed, 41 insertions(+), 3 deletions(-)

Any specific reason you sent this old patch that is already in Linus's
tree out again to everyone?

confused,

greg k-h