Rajat Jain wrote:
Hello Greg / All,
Replying on this thread as I have a small query left regarding this...
-----Original Message-----
From: Greg KH [mailto:greg@xxxxxxxxx]
Sent: Thursday, February 18, 2010 8:23 PM
To: Rajat Jain
Cc: linux-hotplug@xxxxxxxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx
Subject: Re: How does Linux handle PCI-E Surprise unplug?
On Thu, Feb 18, 2010 at 11:35:33AM +0530, Rajat Jain wrote:
Hi,
I'm keen to understand how the Linux kernel handles surprise removal
of
a device, from a PCI-e slot that supports "Hot-plug Surprise"
removal
(in slot capabilities).
Consider that the device in the slot is working normally, with its
driver attached to the device, and is doing all sorts of read /
write
operations on the device registers that have been mapped into the
PCI
memory space. Now when that device is suddenly plugged out (and thus
its
registers suddenly disappear from the PCI memory space), the device
driver is still unaware as it is doing the register reads / writes
on
the device. At this point, IMHO any attempt to access the device
registers will result in an exception (BUS error?) as the device is
gone. Correct?
The driver will suddenly start reading all 0xff and will then need to
abort whatever it was doing. Usually all drivers handle this just
fine
today, as this is what they needed to do when they were pccard
devices.
Nothing new here at all.
Does that mean accessing PCI memory mapped registers for a non-existent
device has effects that are localized ONLY to the driver of that device?
In other words, kernel does not notice or does not even become AWARE
that a driver is trying to access non-existent memory mapped registers?
So trying to access a HW that does not exist is totally legal in that
sense? Is HW NOT supposed to generate an error in this case - as far as
I had read, any access to non existent physical addresses should result
in a bus error ... no?
This will cause Unsupported Request Error. But how it is handled
depends on platform, I think.
Thanks,
Kenji Kaneshige
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