linux-kernel - Re: [PATCH] usb: xhci: Fix incomplete PM resume operation due to XHCI commmand timeout

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Message-ID: <56EFBBD1.6080600@intel.com>
Date:	Mon, 21 Mar 2016 11:16:01 +0200
From:	Mathias Nyman <mathias.nyman@...el.com>
To:	Rajesh Bhagat <rajesh.bhagat@....com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	Sriram Dash <sriram.dash@....com>
Subject: Re: [PATCH] usb: xhci: Fix incomplete PM resume operation due to
 XHCI commmand timeout

On 21.03.2016 06:18, Rajesh Bhagat wrote:
>
>
>>
>> Hi
>>
>> I think clearing the whole command ring is a bit too much in this case.
>> It may cause issues for all attached devices when one command times out.
>>
>
> Hi Mathias,
>
> I understand your point, But I want to understand how would completion handler be called
> if a command is timed out and xhci_abort_cmd_ring is successful. In this case all the code
> would be waiting on completion handler forever.
> 	
>
> 2. xhci_handle_command_timeout -> xhci_abort_cmd_ring(failure) -> xhci_cleanup_command_queue -> xhci_complete_del_and_free_cmd
>
> In our case command is timed out, Hence we hit the case #2 but xhci_abort_cmd_ring is success which
> does not calls complete.

xhci_abort_cmd_ring() will write CA bit (CMD_RING_ABORT) to CRCR register.
This will generate a command completion event with status "command aborted" for the pending command.
This event is then followed by a "command ring stopped" command completion event.

See xHCI specs 5.4.5 and 4.6.1.2

handle_cmd_completion() will check if cmd_comp_code == COMP_CMD_ABORT, goto event_handled, and call
xhci_complete_del_and_free_cmd(cmd, cmd_comp_code) for the aborted command.

If xHCI already processed the aborted command, we might only get a command ring stopped event, in this
case handle_cmd_completion() will call xhci_handle_stopped_cmd_ring(xhci, cmd), which will turn the
commands that were tagged for "abort" that still remain on the command ring to NO-OP commands.

The completion callback will be called for these NO-OP command later when we get a command completion event
for them.

>> What kernel version, and what xhci vendor was this triggered on?
>>
>
> We are using 4.1.8 kernel
>

Are you able to try a more recent version?

-Mathias