Re: [PATCH] Add TPM hardware enablement driver

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To: Greg KH <greg@kroah.com>
Date:	Fri, 08 Apr 2005 15:07:34 -0500

On Tue, 2005-04-05 at 11:14 -0500, Kylene Jo Hall wrote:
> On Thu, 2005-03-24 at 13:33 -0800, Greg KH wrote:
> > On Thu, Mar 24, 2005 at 04:04:25PM -0500, Jeff Garzik wrote:
> > > Greg KH wrote:
> > > >On Tue, Mar 22, 2005 at 09:02:24PM -0500, Jeff Garzik wrote:
> > > >
> > > >>Kylene Hall wrote:
> > > >>
> > > >>>>what is the purpose of this pci_dev_get/put? attempting to prevent
> > > >>>>hotplug or
> > > >>>>something?
> > > >>>
> > > >>>
> > > >>>Seems that since there is a refernce to the device in the chip structure
> > > >>>and I am making the file private data pointer point to that chip
> > > >>>structure this is another reference that must be accounted for. If you
> > > >>>remove it with it open and attempt read or write bad things will happen.
> > > >>>This isn't really hotpluggable either as the TPM is on the motherboard.
> > > >>
> > > >>My point was that there will always be a reference -anyway-, AFAICS.
> > > >>There is a pci_dev reference assigned to the pci_driver when the PCI
> > > >>driver is loaded, and all uses by the TPM generic code of this pointer
> > > >>are -inside- the pci_driver's pci_dev object lifetime.
> > > >
> > > >
> > > >Think of the following situation:
> > > > - driver is bound to device.
> > > > - userspace opens char dev node.
> > > > - device is removed from the system (using fakephp I can do this
> > > > to _any_ pci device, even if it is on the motherboard.)
> > > > - userspace writes to char dev node
> > > > - driver attempts to access pci device structure that is no
> > > > longer present in memory.
> > > >
> > > >Because of this open needs to get a reference to the pci device to
> > > >prevent oopses, or the driver needs to be aware of "device is now gone"
> > > >in some other manner.
> > >
> > > Thanks for explaining; agreed.
> > >
> > > However, there appear to still be massive bugs in this area:
> > >
> > > Consider the behavior of the chrdev if a PCI device has been
> > > unplugged. It's still actively messing with the non-existent
> > > hardware, and never checks for dead h/w AFAICS.
> >
> > I agree, the driver should be fixed to handle this properly.
> >
>

Basically, what I need to figure out is how to solve both issues
simultaneously. I need to not register a pci_driver as I would be
taking over an ID that is not unique to my device as well as get the
hotplugging correct (which i don't know how to do with out a pci_remove
function).

Thanks,

> I have now played with the fakephp driver and have a better
> understanding of these interactions, but I still have questions. With
> the current structure there is a problem because everything is
> "cleaned-up" with the tpm_remove function even if userspace has the
> device open when the tpm's slot is removed and then there are problems
> on subsequent reads/writes. The get/put didn't really stop this from
> happening. Is it right to fix this by cleaning mostly up and placing a
> flag in the read/write path to check for this condition?
>
> This problem actually becomes more complicated. Since the TPM lives on
> the LPC bus and does not have it's own id we were in the process of
> converting the driver to not use a pci_driver structure at all like the
> example in drivers/char/watchdog/i8xx_tco.c. This is desirable so that
> the driver does not claim the id and other drivers can still find their
> devices that also live on the LPC bus and thus share the same ID.
> Without a pci_driver structure there is no probe or remove functions and
> thus the driver is not alerted of the loss of hardware. Any
> recommendations of how to handle this situation?
>
> Thanks,
> Kylie
>

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• Previous message: Tomas Qgren?=: "[2.4] "Fix" introduced in 2.4.27pre2 for bluetooth hci_usb race causes kernel hang"
• In reply to: Kylene Jo Hall: "Re: [PATCH] Add TPM hardware enablement driver"
• Next in thread: Ian Campbell: "Re: [PATCH] Add TPM hardware enablement driver"
• Reply: Ian Campbell: "Re: [PATCH] Add TPM hardware enablement driver"
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