GIC_CPU_MASK_SIMPLE(8)" on big.LITTLE?

[Geert Uytterhoeven]

Hi Liviu,

On Mon, Jan 12, 2015 at 3:45 PM, Liviu Dudau <Liviu.Dudau at arm.com> wrote:
> On Mon, Jan 05, 2015 at 10:37:47AM +0000, Geert Uytterhoeven wrote:
>> A while ago, I wondered:
>>
>> | It's my understanding GIC_CPU_MASK_SIMPLE should reflect the actual number
>> | of CPU cores the interrupt is wired too. Is that correct?
>> |
>> | [Fixes for incorrect masks on shmobile]
>> |
>> | Should it be "GIC_CPU_MASK_SIMPLE(8)" on big.LITTLE configurations
>> | with four Cortex-A15 cores and four Cortex-A7 cores?
>> | Or should the interrupts be delivered to the four Cortex-A15 cores
>> | only by default?
>> |
>> | Note that incorrect masks for GIC PPI interrupts are not limited to
>> | shmobile. Presumably the interrupt specifiers got copied around a lot,
>> | cfr. the proliferation of "GIC_CPU_MASK_SIMPLE(4)" (and the older
>> | hardcoded "0xf0x" variant) in various dtsi files, not always limited to
>> | quad-core CPUs.
>>
>> In the mean time, arch/arm64/boot/dts/arm/juno.dts got added, which has 2 A57
>> cores and 4 A53 cores, and uses GIC_CPU_MASK_SIMPLE(6), so it seems like
>> my two RFC patches to use GIC_CPU_MASK_SIMPLE(8) for 4 A15 cores and 4
>> A7 cores are actually correct?
>>
>> Thanks for your comments!
>>
>> References:
>>   1. Original RFC series:
>>      [PATCH/RFC 0/4] ARM: shmobile: Correct masks for GIC PPI interrupts
>>      http://lists.infradead.org/pipermail/linux-arm-kernel/2014-November/306743.html
>>   2. RFC patches:
>>        a. [PATCH/RFC 3/4] ARM: shmobile: r8a7790: Correct mask for GIC
>> PPI interrupts
>>           http://lists.infradead.org/pipermail/linux-arm-kernel/2014-November/306741.html
>>        b. [PATCH/RFC 4/4] ARM: shmobile: r8a73a4: Correct mask for GIC
>> PPI interrupts
>>           http://lists.infradead.org/pipermail/linux-arm-kernel/2014-November/306740.html

> Your patches are correct, the mask should reflect the number of CPUs present *and* they way
> they are wired in the GIC. AFAIK, HW designers have been sane so far and wired the CPUs
> in sequence in the GIC, but I lack inside knowledge of the shmobile design.

Thanks, I will resend them.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds