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 [thread overview]
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
next prev parent reply other threads:[~2020-05-14 14:40 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-13 21:36 [PATCH] usb: musb: return -ESHUTDOWN in urb when three-strikes error happened 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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