Re: [Qemu-devel] [PATCH RFC] Implement GIC-500 from GICv3 family for arm64

[Shannon Zhao <zhaoshenglong@huawei.com>]

On 2015/3/9 22:41, shlomo.pongratz@toganetworks.com wrote:
> From: Shlomo Pongratz <shlomo.pongratz@huawei.com>
> 
> This patch is a first step toward 128 cores support for arm64.
> 
> At first only 64 cores are supported for two reasons:
> First the largest integer type has the size of 64 bits and modifying
> essential data structures in order to support 128 cores will require
> the usage of bitops.
> Second currently the Linux (kernel) can be configured to support
> up to 64 cores thus there is no urgency with 128 cores support.
> 
> Things left to do:
> 
> Currently the booting Linux may got stuck. The probability of getting stuck
> increases with the number of cores. I'll appreciate core review.
> 
> There is a need to support flexible clusters size. The GIC-500 can support
> up to 128 cores, up to 32 clusters and up to 8 cores is a cluster.
> So for example, if one wishes to have 16 cores, the options are:
> 2 clusters of 8 cores each, 4 clusters with 4 cores each
> Currently only the first option is supported.
> There is an issue of passing clock affinity to via the dtb. In the dtb
> 
> interrupt section there are only 24 bit left to affinity since the
> variable is a 32 bit entity and 8 bits are reserved for flags.
> See Documentation/devicetree/bindings/arm/arch_timer.txt.
> Note that this issue is not seems to be critical as when checking
> /proc/irq/3/smp_affinity with 32 cores all 32 bits are one.
> 
> The last issue is to add support for 128 cores. This requires the usage
> of bitops and currently can be tested up to 64 cores.
> 
> Signed-off-by: Shlomo Pongratz <shlomo.pongratz@toganetworks.com>
> ---
>  hw/arm/Makefile.objs               |    2 +-
>  hw/arm/virtv2.c                    |  774 +++++++++++++++++

Hi,

I think here you want to introduce GICv3 in this patch. So is this necessary to
add a new virtv2 machine? And the codes of this machine mostly are same with virt.

Maybe we can add a parameter such as -GICv3 for machine virt to choose GICv3 for it
and choose GICv2 without this parameter. Then we can reuse more codes.

-- 
Thanks,
Shannon