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From: Mathias Nyman <mathias.nyman@linux.intel.com>
To: Thinh Nguyen <Thinh.Nguyen@synopsys.com>,
	Felipe Balbi <balbi@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-usb@vger.kernel.org,
	Mathias Nyman <mathias.nyman@intel.com>
Cc: John Youn <John.Youn@synopsys.com>
Subject: Re: [PATCH v2 3/7] usb: xhci: Check for blocked disconnection
Date: Tue, 27 Apr 2021 16:08:23 +0300
Message-ID: <845ec8a0-43f2-a28e-5edc-d7a47ccabdf5@linux.intel.com> (raw)
In-Reply-To: <07196754c6de290bb46cc235ce6e96c5df304150.1618014279.git.Thinh.Nguyen@synopsys.com>

Hi Thinh

Sorry about the delay. 

On 10.4.2021 3.47, Thinh Nguyen wrote:
> If there is a device with active enhanced super-speed (eSS) isoc IN
> endpoint(s) behind one or more eSS hubs, DWC_usb31 (v1.90a and prior)
> host controller will not detect the device disconnection until no more
> isoc URB is submitted. If there's a device disconnection, internally
> the wait for tHostTransactionTimeout (USB 3.2 spec 8.13) blocks the
> other endpoints from being scheduled. So, it blocks the interrupt
> endpoint of the eSS hub indicating the port change status.
> 
> This can be an issue for applications that continuously submitting isoc
> URBs to the xHCI. To work around this, stop processing new URBs after 3
> consecutive isoc transaction errors. If new isoc transfers are queued
> after the device is disconnected, the host will respond with USB
> transaction error. After 3 consecutive USB transaction errors, the
> driver can wait a period of time (at least 2 * largest periodic interval
> of the topology) without ringing isoc endpoint doorbell to detect the
> port change status. If there is no disconnection detected, ring the
> endpoint doorbell to resume isoc transfers.

Is that enough? many Isoc URBs queue 16 - 32 Isoc TRBs per URB.
And drivers like UVC queue several URBs in advance.

If I remember correctly then a transaction errors won't stop Isoch endpoints,
so waiting for 2 * Interval after 3 consecutive transaction errors might not
be enough.

How about stopping the endpoint after 3 consecutive transaction errors,
and restating it a bit later? 

> 
> This workaround tracks the max eSS periodic interval every time there's
> an endpoint added or dropped, which happens when there's bandwidth
> check. So, scan the topology and update the xhci->max_ess_interval
> whenever there's a bandwidth check. Introduced a new flag
> VDEV_DISCONN_CHECK_PENDING to prevent ringing the doorbell while waiting
> for a disconnection status. After 2 * max_ess_interval time and no
> disconnection detected, a delayed work will ring the doorbell to resume
> the active isoc transfers.

Sounds very elaborate for a vendor specific disconnect workaround.
Isn't there a simpler way?

Maybe stop all isoc in endpoints if one them has 3 consecutive transaction error,
wait for 2x hub interrupt interval time, and then restart the endpoints if there is
no disconnect?

There is bigger concern with this series, it scatters a lot of vendor specific code 
around the generic xhci driver. It's not very clear afterwards what code is part of the
workaround and what is generic code.

We just got a lot of the Mediatek code moved to xhci-mtk*, maybe its time to add xhci-snps.c
instead of using the generic platform driver with tons of workarounds and quirks.

Thanks
-Mathias    


  reply index

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-09  1:41 [PATCH 0/6] usb: Set quirks for xhci/dwc3 host mode Thinh Nguyen
2021-04-09  1:41 ` [PATCH 1/6] usb: xhci: Move quirks definitions to common usb header Thinh Nguyen
2021-04-09  6:50   ` Greg Kroah-Hartman
2021-04-09  8:01     ` Thinh Nguyen
2021-04-09 16:26   ` kernel test robot
2021-04-09 19:54   ` kernel test robot
2021-04-09  1:42 ` [PATCH 2/6] usb: xhci: Check for blocked disconnection Thinh Nguyen
2021-04-09  1:42 ` [PATCH 3/6] usb: xhci: Workaround undercalculated BW for fullspeed BI Thinh Nguyen
2021-04-09  1:42 ` [PATCH 4/6] usb: xhci: Rename Compliance mode timer quirk Thinh Nguyen
2021-04-09  1:42 ` [PATCH 5/6] usb: xhci: Workaround lost disconnect port status Thinh Nguyen
2021-04-09  1:42 ` [PATCH 6/6] usb: dwc3: host: Set quirks base on version Thinh Nguyen
2021-04-09  6:53   ` Greg Kroah-Hartman
2021-04-09  8:01     ` Thinh Nguyen
2021-04-09 13:22       ` Greg Kroah-Hartman
2021-04-10  0:44         ` Thinh Nguyen
2021-04-10  0:46 ` [PATCH v2 0/7] usb: Set quirks for xhci/dwc3 host mode Thinh Nguyen
2021-04-10  0:46   ` [PATCH v2 1/7] usb: xhci: Move quirks definitions to common usb header Thinh Nguyen
2021-04-10  0:46   ` [PATCH v2 2/7] usb: xhci: Move xhci-plat header " Thinh Nguyen
2021-04-10  0:47   ` [PATCH v2 3/7] usb: xhci: Check for blocked disconnection Thinh Nguyen
2021-04-27 13:08     ` Mathias Nyman [this message]
2021-04-27 22:30       ` Thinh Nguyen
2021-04-28 13:32         ` Mathias Nyman
2021-04-29  0:54           ` Thinh Nguyen
2021-04-10  0:47   ` [PATCH v2 4/7] usb: xhci: Workaround undercalculated BW for fullspeed BI Thinh Nguyen
2021-04-28 11:57     ` Mathias Nyman
2021-04-10  0:47   ` [PATCH v2 5/7] usb: xhci: Rename Compliance mode timer quirk Thinh Nguyen
2021-04-10  0:47   ` [PATCH v2 6/7] usb: xhci: Workaround lost disconnect port status Thinh Nguyen
2021-04-28 13:48     ` Mathias Nyman
2021-04-29  1:00       ` Thinh Nguyen
2021-04-10  0:47   ` [PATCH v2 7/7] usb: dwc3: host: Set quirks base on version Thinh Nguyen
2021-04-19 21:07   ` [PATCH v2 0/7] usb: Set quirks for xhci/dwc3 host mode Thinh Nguyen

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