linux-kernel - Re: [linux-usb-devel] [PATCH] Fix NEC OHCI chip silicon bug

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Message-ID: <20070604210555.GB12676@hansmi.ch>
Date:	Mon, 4 Jun 2007 23:05:55 +0200
From:	Michael Hanselmann <linux-kernel@...smi.ch>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	linux-kernel@...r.kernel.org, dbrownell@...rs.sourceforge.net,
	linux-usb-devel@...ts.sourceforge.net,
	linux-kernel@...lerfox.forkbomb.ch
Subject: Re: [linux-usb-devel] [PATCH] Fix NEC OHCI chip silicon bug

On Sat, Jun 02, 2007 at 10:49:44AM -0400, Alan Stern wrote:
> Then later on, when the hub driver is resumed it will see the flag and
> disconnect all the devices below the root hub.

> For instance, you could force ohci-hcd to report connect-change events
> on all the ports. Perhaps it does something like that anyway, in which
> case you wouldn't have to worry about it.

After studying the code for two evenings, I'm quite sure it does that
already.

A comment in ohci-hcd.c:ohci_restart reads:
  /* mark any devices gone, so they do nothing till khubd disconnects.
   * recycle any "live" eds/tds (and urbs) right away.
   * later, khubd disconnect processing will recycle the other state,
   * (either as disconnect/reconnect, or maybe someday as a reset).
   */

usb_root_hub_lost_power marks the ports as gone, khubd will disconnect them.
After restarting the chip, khubd will cause them to be detected again.

This is also what I can watch in the logs:
  ohci_hcd 0001:10:15.1: OHCI Unrecoverable Error, scheduling NEC chip restart
  usb usb2: root hub lost power or was reset
  usb 2-2: USB disconnect, address 2
  input: appletouch disconnected
  usb 2-2: new full speed USB device using ohci_hcd and address 3
  usb 2-2: configuration #1 chosen from 1 choice
  input: Apple Computer Apple Internal Keyboard / Trackpad as /class/input/input16 on usb-0001:10:15.1-2
  input: appletouch as /class/input/input17
  input: Apple Computer Apple Internal Keyboard / Trackpad as /class/input/input18 on usb-0001:10:15.1-2

(Actually, I added some code to trigger the error handling code, reliably
reproducing it otherwise is impossible.)

Thanks,
Michael
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