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From: Lu Baolu <baolu.lu@linux.intel.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Mathias Nyman <mathias.nyman@linux.intel.com>,
	Ingo Molnar <mingo@redhat.com>,
	tglx@linutronix.de, linux-usb@vger.kernel.org, x86@kernel.org,
	linux-kernel@vger.kernel.org, Jiri Slaby <jslaby@suse.cz>
Subject: Re: [PATCH v5 1/4] usb: dbc: early driver for xhci debug capability
Date: Thu, 9 Feb 2017 13:59:01 +0800	[thread overview]
Message-ID: <589C0525.3050006@linux.intel.com> (raw)
In-Reply-To: <20170126071937.GA3399@gmail.com>

Hi Ingo,

On 01/26/2017 03:19 PM, Ingo Molnar wrote:
> * Lu Baolu <baolu.lu@linux.intel.com> wrote:
>
>> Fair enough.
>>
>> USB connection is stable enough, unless the user unplugs the
>> USB cable during debugging.
> What does the hardware do in this case? The XHCI registers are in the host 
> hardware, so they won't disappear, right? Is there some cable connection status 
> bit we can extract without interrupts?

The hardware has a register for the debug port status. Software is able to
check cable unplugging through this register.

>
> I.e. if there's any polling component then it would be reasonable to add an error 
> component: poll the status and if it goes 'disconnected' then disable early-printk 
> altogether in this case and trigger an emergency printk() so that there's chance 
> that the user notices [if the system does not misbehave otherwise].

Sure. I will add a kernel thread to polling the errors. I will show you the
code in the new upcoming version.

Best regards,
Lu Baolu

>
> I.e. try to be as robust and informative as lockdep - yet don't lock up the host 
> kernel: lockdep too is called from very deep internals, there are various 
> conditions where it sees corrupt data structures (i.e. a 'disconnect' - a system 
> environment outside the normal bounds of operation), yet of the kernel and over 
> the last 10+ years of lockdep's existence we had very, very few cases of lockdep 
> itself locking up and behaving unpredictably.
>
> Thanks,
>
> 	Ingo
>

  parent reply	other threads:[~2017-02-09  5:59 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-11-15  6:02 [PATCH v5 0/4] usb: early: add support for early printk through USB3 debug port Lu Baolu
2016-11-15  6:02 ` [PATCH v5 1/4] usb: dbc: early driver for xhci debug capability Lu Baolu
2017-01-19  9:37   ` Ingo Molnar
2017-01-20  2:47     ` Lu Baolu
2017-01-22  9:04       ` Ingo Molnar
2017-01-24  4:44         ` Lu Baolu
2017-01-24  8:20           ` Ingo Molnar
2017-01-25  5:28             ` Lu Baolu
2017-01-25  9:23               ` Ingo Molnar
2017-01-25  9:57                 ` Peter Zijlstra
2017-01-25 12:27                   ` Lu Baolu
2017-01-25 14:38                     ` Peter Zijlstra
2017-01-25 15:51                       ` Lu Baolu
2017-01-25 16:16                         ` Peter Zijlstra
2017-01-26  3:37                           ` Lu Baolu
2017-01-26  7:19                             ` Ingo Molnar
2017-01-26  7:49                               ` Lu Baolu
2017-01-26  8:17                                 ` Ingo Molnar
2017-01-26 10:28                               ` Peter Zijlstra
2017-01-26 16:01                                 ` Ingo Molnar
2017-01-26 17:39                                   ` Peter Zijlstra
2017-01-27  6:51                                     ` Ingo Molnar
2017-02-09  5:59                               ` Lu Baolu [this message]
2017-01-26  7:22                         ` Ingo Molnar
2017-02-09  7:37                           ` Lu Baolu
2017-01-25 12:17                 ` Lu Baolu
2017-01-26  3:26                 ` Lu Baolu
2016-11-15  6:02 ` [PATCH v5 2/4] x86: add support for earlyprintk via USB3 debug port Lu Baolu
2017-01-19  9:38   ` Ingo Molnar
2017-01-20  2:48     ` Lu Baolu
2016-11-15  6:02 ` [PATCH v5 3/4] usb: serial: usb_debug: add support for dbc debug device Lu Baolu
2017-01-19  9:39   ` Ingo Molnar
2017-01-20  2:50     ` Lu Baolu
2016-11-15  6:02 ` [PATCH v5 4/4] usb: doc: add document for USB3 debug port usage Lu Baolu
2017-01-19  9:41   ` Ingo Molnar
2017-01-20  2:53     ` Lu Baolu
2017-01-18  6:20 ` [PATCH v5 0/4] usb: early: add support for early printk through USB3 debug port Lu Baolu
2017-01-19  9:06   ` Greg Kroah-Hartman
2017-01-19  9:09     ` Ingo Molnar
2017-01-19 11:24       ` Mathias Nyman
2017-01-19  9:12 ` Ingo Molnar
2017-01-20  2:56   ` Lu Baolu

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