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

[Philippe Bergheaud]

On 07/11/2017 21:18, Benjamin Herrenschmidt wrote:
> 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.

Got it.

One last question, though: should we define CMPM indication and mask
values in skiboot and Linux, or should we add a skiboot API to tell Linux?

Philippe