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Message-ID: <54DDBBB0.7070602@linux.intel.com>
Date:	Fri, 13 Feb 2015 10:54:08 +0200
From:	Mathias Nyman <mathias.nyman@...ux.intel.com>
To:	Alan Stern <stern@...land.harvard.edu>,
	Mathias Nyman <mathias.nyman@...el.com>,
	Sneeker Yeh <sneeker.yeh@...il.com>
CC:	Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Grant Likely <grant.likely@...aro.org>,
	Huang Rui <ray.huang@....com>,
	Kishon Vijay Abraham I <kishon@...com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org, linux-omap@...r.kernel.org,
	Andy Green <andy.green@...aro.org>,
	Jassi Brar <jaswinder.singh@...aro.org>,
	Sneeker Yeh <Sneeker.Yeh@...fujitsu.com>
Subject: Re: [PATCH v3 1/5] xhci: add a quirk for device disconnection errata
 for Synopsis Designware USB3 core

On 12.02.2015 17:18, Alan Stern wrote:
> On Thu, 12 Feb 2015, Mathias Nyman wrote:
> 
>> On 25.01.2015 10:13, Sneeker Yeh wrote:
>>> This issue is defined by a three-way race at disconnect, between
>>> 1) Class driver interrupt endpoint resheduling attempts if the ISR gave an ep
>>>    error event due to device detach (it would try 3 times)
>>> 2) Disconnect interrupt on PORTSC_CSC, which is cleared by hub thread
>>>    asynchronously
>>> 3) The hardware IP was configured in silicon with
>>>    - DWC_USB3_SUSPEND_ON_DISCONNECT_EN=1
>>>    - Synopsys IP version is < 3.00a
>>> The IP will auto-suspend itself on device detach with some phy-specific interval
>>> after CSC is cleared by 2)
>>>
>>> If 2) and 3) complete before 1), the interrupts it expects will not be generated
>>> by the autosuspended IP, leading to a deadlock. Even later disconnection
>>> procedure would detect that corresponding urb is still in-progress and issue a
>>> ep stop command, auto-suspended IP still won't respond to that command.
> 
> If the Synopsys IP provides a way to do it, it would be better to turn
> off the autosuspend feature entirely.  Doesn't autosuspend violate the
> xHCI specification?
> 
>> So did I understand correctly that the class driver submits a new urb which
>> is enqueued by xhci_urb_enqueue() before the hub thread notices the device is disconnected.
>> Then hub thread clears CSC bit, controller suspends and the new urb is never given back?
>>
>> Doesn't the CSC bit and PORT_CONNECT bit show the device is disconnected when we enter
>> xhci_enqueue_urb(), even it the hub thread doesn't know this yet?
> 
> What if the device disconnects _after_ the new URB is enqueued?

True, those URBs would be left hanging.

So if possible, tweaking the Synopsis autosuspend feature would be nicer.

If its not possible then I guess a quirk patch like this will do.

-Mathias


 



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