[Skiboot] [PATCH 1/2] phb4: set PHB CMPM registers for tunneled operations

[Benjamin Herrenschmidt]

On Tue, 2017-11-07 at 14:19 +0100, Philippe Bergheaud wrote:
> The ASN/CAPI CMPM indications are currently hard coded in skiboot and
> Linux. This patch aims at avoiding a firmware update if ever one of
> these values has to be changed in the future. With this patch, a Linux
> kernel update would suffice. (Actually, the patch should allow changing
> ASN and CAPI CMPM masks also.)
> 
> This patch is not mandatory. We can drop it and live with the current
> static implementation, if we assume that those values will never change.

A firmware update is a LOT easier to deploy than a kernel update in
practice. We have more control on the firmware and it's update
schedule, at least for IBM systems, while a kernel update requires
synchronizing with all distros and can be really hard to deploy.

Also, this puts too much knowledge about the HW layout in Linux, which
could be problematic if we have to change things in a future chip as we
are aiming for full backward compatibility.

Cheers,
Ben.