Re: Memory mapping PCI memory region to user space

[David Hawkins <dwh@ovro.caltech.edu>]

> Why don't use the mmap file exposed by sysfs so you dont have to  
> write your own code?
> 
> See Documentation/filesystems/sysfs-pci.txt.  But effectively down  
> under /sys/bus/pci/devices/[domain:bus:dev:func]/ you will get  
> resource[0..N-1] that corresponds to each BAR on the device.  This is  
> a mmap file to access that region.

Hi Kumar,

Most likely he didn't know about it, I didn't :)

When I was testing the Yosemite board as the host, I found
that I could set the endian flag on the mmapped page, which
then made the PCI device registers read as 32-bit quantities
read back with the same layout under both x86 and PPC
hosts.

So, if someone planned on using that 'feature', that would
be a reason for writing your own mmap() implementation.
I didn't see any option in the sysfs file for setting that
page flag (but, I didn't look around in other sysfs files).

Thanks for the pointer to the sysfs node!

Cheers
Dave