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Re: [PATCH 0/5] gicv3: Use right number of prio bits for the CPU


From: Richard Henderson
Subject: Re: [PATCH 0/5] gicv3: Use right number of prio bits for the CPU
Date: Sat, 7 May 2022 06:35:39 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0

On 5/6/22 11:21, Peter Maydell wrote:
This patchset fills in an odd inconsistency in our GICv3 emulation
that I noticed while I was doing the GICv4 work. At the moment we
allow the CPU to specify the number of bits of virtual priority
(via the ARMCPU::gic_vpribits field), but we always use 8 bits of
physical priority, even though to my knowledge no real Arm CPU
hardware has that many.

This series makes the GICv3 emulation use a runtime-configurable
number of physical priority bits, and sets it to match the number
used by the various CPUs we implement (which is 5 for all the
Cortex-Axx CPUs we emulate). Because changing the number of
priority bits is a migration compatibility break, we use a compat
property to keep the number of priority bits at 8 for older
versions of the virt board.

There is one TODO left in this series, which is that I don't know
the right value to use for the A64FX, so I've guessed that it
is 5, like all the Arm implementations.

Patch 1 is an independent bugfix; patch 5 is cleanup.

thanks
-- PMM

Peter Maydell (5):
   hw/intc/arm_gicv3: report correct PRIbits field in ICV_CTLR_EL1
   hw/intc/arm_gicv3_kvm.c: Stop using GIC_MIN_BPR constant
   hw/intc/arm_gicv3: Support configurable number of physical priority
     bits
   hw/intc/arm_gicv3: Use correct number of priority bits for the CPU
   hw/intc/arm_gicv3: Provide ich_num_aprs()


Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~




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