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From: Bin Liu <b-liu@ti.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: <linux-usb@vger.kernel.org>
Subject: Re: [PATCH] usb: musb: return -ESHUTDOWN in urb when three-strikes error happened
Date: Thu, 14 May 2020 09:28:03 -0500
Message-ID: <20200514142803.GA11463@iaqt7> (raw)
In-Reply-To: <20200514013205.GA10515@rowland.harvard.edu>

On Wed, May 13, 2020 at 09:32:05PM -0400, Alan Stern wrote:
> On Wed, May 13, 2020 at 04:36:20PM -0500, Bin Liu wrote:
> > When a USB device attached to a hub got disconnected, MUSB controller
> > generates RXCSR_RX_ERROR interrupt for the 3-strikes-out error.
> > 
> > Currently the MUSB host driver returns -EPROTO in current URB, then the
> > USB device driver could immediately resubmit the URB which causes MUSB
> > generate RXCSR_RX_ERROR interrupt again. This circle causes interrupt
> > storm then the hub never got a chance to report the USB device detach.
> > 
> > To fix the interrupt storm, change the URB return code to -ESHUTDOWN for
> > MUSB_RXCSR_H_ERROR interrupt, so that the USB device driver will not
> > immediately resubmit the URB.
> > 
> > Signed-off-by: Bin Liu <b-liu@ti.com>
> 
> Strictly speaking, this is not the right thing to do.  It goes against 
> the API described in error-codes.rst.  A better approach would be to fix 

error-codes.rst says:

-ESHUTDOWN              The device or host controller has been
			disabled due to some problem that could not
			be worked around, such as a physical
			disconnect.

So -ESHUTDOWN is applicable in this case - the device is disconnected
behind a hub.

> the drivers that immediately resubmit an URB after getting a -EPROTO 

This has been discussed before [1]. And John indicated there are many
device drivers do not delay when resubmitting after getting -EPROTO [2],
and it is quite bit of work to fix it in all device drivers [3]. So
better to solve the issue in HCD.

> error.  After all, that is the wrong thing to do no matter what sort of 
> host controller the device is attached to.

[1] https://www.spinics.net/lists/linux-usb/msg175292.html
[2] https://www.spinics.net/lists/linux-usb/msg176327.html
[3] https://www.spinics.net/lists/linux-usb/msg176375.html

-Bin.

  reply index

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-13 21:36 Bin Liu
2020-05-14  1:32 ` Alan Stern
2020-05-14 14:28   ` Bin Liu [this message]
2020-05-14 14:40     ` Alan Stern
2020-05-14 15:02       ` Bin Liu
2020-05-14 15:37         ` Bin Liu
2020-05-14 16:26           ` Alan Stern
2020-05-14 17:00             ` Bin Liu
2020-05-14 18:55               ` Alan Stern
2020-05-19 17:12                 ` Bin Liu
2020-05-19 20:01                   ` Alan Stern
2020-05-20 14:31                     ` Bin Liu
2020-05-20 16:40                       ` Alan Stern
2020-05-20 18:05                         ` Bin Liu
2020-05-20 18:25                           ` Alan Stern
2020-05-20 18:59                             ` Bin Liu
2020-05-19 17:28             ` [PATCH v2] " Bin Liu

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