Re: [PATCH] USB: EHCI: don't reread PORTSC after disabling port power

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On Sun, 22 Oct 2017, Uwe [iso-8859-1] Kleine-K� wrote:

> Hello,
> 
> On Sat, Oct 21, 2017 at 11:08:39AM -0400, Alan Stern wrote:
> > On Fri, 20 Oct 2017, Uwe [iso-8859-1] Kleine-K� wrote:
> > > On Fri, Oct 20, 2017 at 03:47:37PM -0400, Alan Stern wrote:
> > > > On Fri, 20 Oct 2017, Uwe [iso-8859-1] Kleine-K� wrote:
> > > > > On Fri, Oct 20, 2017 at 05:27:09PM -0200, Fabio Estevam wrote:
> > > > > > On Fri, Oct 20, 2017 at 5:20 PM, Uwe Kleine-K�
> > > > > > <u.kleine-koenig@xxxxxxxxxxxxxx> wrote:
> > > > > > 
> > > > > > > It also works. However I wonder if it's right that I'm spammed by
> > > > > > > over-current messages now (independent of which fix I choose) as long as
> > > > > > > there is something connected to the port that draws too much power:
> > > > > > >
> > > > > > >         [   53.406833] usb usb1-port1: over-current condition
> > > > > > >         [   53.631749] usb usb1-port1: over-current condition
> > > > > > >         [   53.856720] usb usb1-port1: over-current condition
> > > > > > >         [   54.081732] usb usb1-port1: over-current condition
> > > > > > >         [   54.306727] usb usb1-port1: over-current condition
> > > > > > >         [   54.531722] usb usb1-port1: over-current condition
> > > > > > >         [   54.756722] usb usb1-port1: over-current condition
> > > > > > >
> > > > > > > It seems to be intended or am I missing something?
> > > > 
> > > > Well, it does report a potentially hardware-damaging condition.  But 
> > > > you are right that excessive repetition doesn't do any good.
> > > > 
> > > > Maybe we should keep track of the time interval between overcurrent
> > > > events on each port.  If we see more than one event in a 10-second
> > > > window, leave the port permanently powered-off.  (But then how would we
> > > > recover?)
> > > 
> > > Maybe double the interval each time up to a maximum of 1 minute?
> > 
> > I guess spamming the log once a minute is better than spamming it four 
> > times a second.  But it's still spam.  If people don't react to the 
> > error situation by removing the cause of the overcurrent, repeating the 
> > message over and over won't help much.
> > 
> > We could keep a per-port is_overcurrent flag.  If the port has an
> > overcurrent status and the flag is clear, log the error and set the
> > flag.  If the port doesn't have an overcurrent status, clear the flag.  
> > In other words, report each overcurrent event only once.
> 
> You need to be a bit clever here. As reaction to the over-current event
> the port's power is cut which makes the event go away. Then after
> reenabling power it takes some time (typically 3 ms) until the Micrel
> 2025 signals over-current again.

That's right.  It might be better to use an even longer timeout, like
1000 ms.  Would you like to write a patch to do this?

Alan Stern

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