linux-kernel - Re: [PATCH v4 02/26] arm64: cpufeature: Add cpufeature for IRQ priority masking

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Message-ID: <b0673d7e-9a1e-7dcb-5322-c05fe0821349@arm.com>
Date:   Fri, 25 May 2018 11:17:45 +0100
From:   Julien Thierry <julien.thierry@....com>
To:     Suzuki K Poulose <Suzuki.Poulose@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, daniel.thompson@...aro.org,
        joel@...lfernandes.org, marc.zyngier@....com, mark.rutland@....com,
        christoffer.dall@....com, james.morse@....com,
        catalin.marinas@....com, will.deacon@....com
Subject: Re: [PATCH v4 02/26] arm64: cpufeature: Add cpufeature for IRQ
 priority masking

On 25/05/18 11:04, Suzuki K Poulose wrote:
> On 25/05/18 10:49, Julien Thierry wrote:
>> Add a cpufeature indicating whether a cpu supports masking interrupts
>> by priority.
> 
> How is this different from the SYSREG_GIC_CPUIF cap ? Is it just
> the description ?

More or less.

It is just to have an easier condition in the rest of the series. 
Basically the PRIO masking feature is enabled if we have a GICv3 CPUIF 
working *and* the option was selected at build time. Before this meant 
that I was checking for the GIC_CPUIF cap inside #ifdefs (and putting 
alternatives depending on that inside #ifdefs as well).

Having this as a separate feature feels easier to manage in the code. It 
also makes it clearer at boot time that the kernel will be using irq 
priorities (although I admit it was not the initial intention):

[    0.000000] CPU features: detected: IRQ priority masking

But yes that new feature will be detected only if SYSREG_GIC_CPUIF gets 
detected as well.

Cheers,

-- 
Julien Thierry