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From: Alan Stern <stern@rowland.harvard.edu>
To: Bin Liu <b-liu@ti.com>, linux-usb@vger.kernel.org
Subject: Re: [PATCH] usb: musb: return -ESHUTDOWN in urb when three-strikes error happened
Date: Thu, 14 May 2020 10:40:53 -0400
Message-ID: <20200514144053.GC12181@rowland.harvard.edu> (raw)
In-Reply-To: <20200514142803.GA11463@iaqt7>

On Thu, May 14, 2020 at 09:28:03AM -0500, Bin Liu wrote:
> 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.

Yes, but you don't _know_ that the device was disconnected.  All you 
know is that there was a 3-strikes error.  Other problems can cause such 
errors (noise, for example).

Alan Stern

  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
2020-05-14 14:40     ` Alan Stern [this message]
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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