Map PCI resource to user space problem.

From: Armin Schindler
Date: Mon Jun 20 2011 - 05:45:51 EST


when I try to map PCI resource of size < PAGE_SIZE to user space
with e.g. remap_pfn_range() the mapping seems to be created,
but the access to the PCI device just doesn't work (read returns 0xff).

The same happens when using sysfs. The device has
# ls -al /sys/bus/pci/devices/0000\:02\:09.0/resource*
-rw------- 1 root root 512 Jun 20 11:33 /sys/bus/pci/devices/0000:02:09.0/resource0
-rw------- 1 root root 256 Jun 20 11:33 /sys/bus/pci/devices/0000:02:09.0/resource1
-rw------- 1 root root 8388608 Jun 20 11:33 /sys/bus/pci/devices/0000:02:09.0/resource2
-rw------- 1 root root 262144 Jun 20 11:33 /sys/bus/pci/devices/0000:02:09.0/resource3

and when I mmap() resource0, a valid address is returned, but reading the area always returns 0xff.

Since a kernel driver can access resource0 here without problems when using
ioremap(), I'm not sure what is wrong with the sysfs entry for user space
(or using remap_pfn_range() in own mmap function).
The only hint I have so far is the size, which is smaller than PAGE_SIZE.

What would be the correct way to map this area to user space?

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