Subject: Re: sudden detach
To: Bill Studenmund <>
From: Garrett D'Amore <>
List: tech-kern
Date: 07/12/2006 07:41:59
Bill Studenmund wrote:
> On Wed, Jul 12, 2006 at 07:19:27AM -0700, Garrett D'Amore wrote:
>> John Nemeth wrote:
>>> On Dec 1,  7:38am, "Garrett D'Amore" wrote:
>>> } drivers are generally _not_ hotplug safe.
>>>      What about PCI Hot-Plug?  Sounds to me that if drivers can't
>>> handle sudden detach now, they will need to do so in the future.
>> All PCI hotplug systems that I'm familiar with use a command to
>> deconfigure the device before removal first.  CompactPCI even has LEDs
>> to indicate "safe-to-remove" status, IIRC.
>> So in  the case of PCI, you _don't_ deal with "sudden detach".  You deal
>> with "controlled, prenotified detach".
> The deep problem I see with this is that, as long as the cards do not have 
> physical latches controlled by the OS, you will never be able to totally 
> prevent unexpected removal. :-(
> I agree it _shouldn't_ happen, and I agree we should be grumpy about it. 
> But I think we should be able to cope with sudden removal.

I think in the case of CompactPCI there can be latches to prevent it,
and further, I am not entirely convinced that removal of CompactPCI
cards _without_ doing the appropriate shutdown commands is
_electrically_ safe.  I.e. I am not sure we can do anything in software
to _make_ sudden removal safe in the case of hotplug PCI.

Quentin's question about express card is well taken though -- I don't
know anything about that standard.  I suspect it has similar semantics
as cardbus, but that's just an educated guess on my part.

    -- Garrett
> Take care,
> Bill

Garrett D'Amore, Principal Software Engineer
Tadpole Computer / Computing Technologies Division,
General Dynamics C4 Systems
Phone: 951 325-2134  Fax: 951 325-2191