Re: [Xen-devel] [PATCH V6 03/10] xen/arm: Use the new functions for vCPUID/vaffinity transformation

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Fri, 2015-06-05 at 19:18 +0100, Julien Grall wrote:
> On 05/06/2015 16:56, Ian Campbell wrote:
> > On Mon, 2015-06-01 at 20:56 +0800, Chen Baozi wrote:
> >> From: Chen Baozi <baozich@xxxxxxxxx>
> >>
> >> There are 3 places to change:
> >>
> >> * Initialise vMPIDR value in vcpu_initialise()
> >> * Find the vCPU from vMPIDR affinity information when accessing GICD
> >>    registers in vGIC
> >> * Find the vCPU from vMPIDR affinity information when booting with vPSCI
> >>    in vGIC
> >>    - Also make the code for PSCI 0.1 use MPIDR-like value as the cpuid.
> >
> > Does this "- Also ..." not need to be done at the same time as the
> > change to how we describe things in the FDT? Since that is where the
> > guest gets the parameter from, isn't it?
> 
> Well, we only support 8 CPUs.

I was assuming this would change later in the patch. I don't think PSCI
0.1 is limited to gic v2, is it? (If it is then this is worth mentioning
in the commit message too)

>  So this changes will return the same value 
> as before. It may be worth to mention it.
> 
> In another side, both PSCI 0.1 and PSCI 0.2 are modified to respect the 
> MPIDR like within this patch. The working in the commit message may be 
> misleading.

Yes, possibly.

> Somehow the code path slightly differ when the PSCI 0.2 for guest has 
> been added. The spec says (PSCI 0.1 Section 6.3 (ARM DEN 0022A)):
> 
> "Ideally platform discovery mechanism such as firmware tables would be
> used by secure firmware to describe the set of valid CPUIDs to the
> hypervisor or Rich OS, if the former is not present. The hypervisor in
> turn can create and supply virtual discovery mechanisms to its guests.""
> 
> I interpreted this as CPUID is equal to the "reg" register in DT (which 
> is an MPIDR-like value).
> 
> FWIW, this is the interpretation made by Linux too.

Documentation/devicetree/bindings/arm/cpus.txt requires it to be the
MPIDR value on armv7 and v8.

Ian.


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