Re: [PATCH] usb: musb: return -ESHUTDOWN in urb when three-strikes error happened

[Bin Liu <b-liu@ti.com>]

On Thu, May 14, 2020 at 12:26:04PM -0400, Alan Stern wrote:
> On Thu, May 14, 2020 at 10:37:31AM -0500, Bin Liu wrote:
> > On Thu, May 14, 2020 at 10:02:59AM -0500, Bin Liu wrote:
> > > On Thu, May 14, 2020 at 10:40:53AM -0400, Alan Stern wrote:
> > > > 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).
> > > 
> > > Yes, I know this. But we don't have a solution then. I cannot add
> > > resubmit delay in those ~500 device drivers.
> > 
> > By the way I don't think noise could last long enough to cause 3-strikes
> > error. A shortest USB packet is about 3-bytes long, a noise should be
> > just a glitch, it won't last at least 3-bytes long to supress the bus
> > and 3 times on the exact timing when the host expecting a response
> > packet. I cannot think of any other reason which can cause the 3-strikes
> > error other than the device is off the bus.
> 
> Heh.  I heard from somebody (many years ago) about a setup where one of 
> his USB devices stopped working whenever he turned on the fluorescent 
> lights.

This could happen, noise comming in from the power supply, cheap power
supply and poor board design.

> Yes, I agree that noise is pretty uncommon, and the vast majority of 
> 3-strikes errors are caused by disconnection or device firmware bugs.  

I wasn't mean noise is uncommon, it is just it won't cause 3-strikes
error because the glitch is very short. I have seen many cases that
noise causing issues on MUSB due to poor board design especially on
those USB modem or WIFI projects.

> That's why I didn't NAK this patch.

Thanks.

> Still, it's worth pointing out that this change abuses the API (perhaps 
> mentioning it in a comment).  And it still would be preferable to fix 

Okay, I will add those notes in comment in v2.

> the drivers in question, impractical though that may be.  (I have a hard 
> time believing there are really 500 of them getting this wrong...)

I am not sure about it either, but yeah it is not practical to fix the
issue in device drivers. So far I have seen 3 reports of this issue:

1. with FTDI usb-serial adapter, the issue is in the usb serial generic
driver;

2. with a modem, the issue is in usb wwan driver as I fixed in the patch
I sent yesterday;

2. another modem, before I was able to locate the offending device
driver, the guy who reported the issue disappeared, and not responding
me.

-Bin.