On Fri, Oct 30, 2015 at 06:32:54PM +0000, Julien Grall wrote:

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Ugh! I though that it is a requirement that every memory/io region user
must register it using relevant function. It looks that it is not true.
So, there is only one reliable way to get info about used io/memory regions.
You must look at DT. However, if driver may agree with a device other
config and move used io/memory regions to different place without updating
DT then we are lost.

While the Linux folks are trying to describe all the device in the
Device Tree, it not always the case.

Also, browsing the device tree to find memory range is a pain and quite
fragile. For instance we already do that in the hypervisor to map all
the device to DOM0 (see arch/arm/domain_build.c) but we still do have
bug report of platform not working with this solution.

I expected this. Do we have any other choice? Maybe we should discuss
this on wider forum somewhere and encourage devs to use relevant resource
management functions in drivers. Well, I saw somewhere that IanC doubts
it is feasible but I do not see better solution for this right now.

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TBH I don't see why you don't hit this issue on x86. Overall some of the
drivers can be shared between the 2 architectures.

Are you able to point out any (x86) driver which does not behave as it should?

Just thinking that on x86 you have the e820 which describe the memory
layout of the platform.

Am I correct to say that every I/O regions are described in the e820 and
therefore registered when Linux is booting?

No, as I saw regions used by devices are not listed on some (all?) machines.
I have a feeling that driver negotiates with device where a given I/O
region should be placed. So, this region is not known by BIOS or even UEFI
in advance. Sadly, I do not know in detail how this process works.

Daniel