linux-kernel - Re: [PATCH v7] arm64: Add support for new control bits CTR_EL0.DIC and CTR

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Date:   Fri, 9 Mar 2018 13:48:13 +0000
From:   Will Deacon <will.deacon@....com>
To:     Shanker Donthineni <shankerd@...eaurora.org>
Cc:     Robin Murphy <robin.murphy@....com>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        kvmarm <kvmarm@...ts.cs.columbia.edu>,
        Marc Zyngier <marc.zyngier@....com>,
        Vikram Sethi <vikrams@...eaurora.org>,
        Philip Elcan <pelcan@...eaurora.org>
Subject: Re: [PATCH v7] arm64: Add support for new control bits CTR_EL0.DIC
 and CTR_EL0.IDC

On Wed, Mar 07, 2018 at 09:00:08AM -0600, Shanker Donthineni wrote:
> The DCache clean & ICache invalidation requirements for instructions
> to be data coherence are discoverable through new fields in CTR_EL0.
> The following two control bits DIC and IDC were defined for this
> purpose. No need to perform point of unification cache maintenance
> operations from software on systems where CPU caches are transparent.
> 
> This patch optimize the three functions __flush_cache_user_range(),
> clean_dcache_area_pou() and invalidate_icache_range() if the hardware
> reports CTR_EL0.IDC and/or CTR_EL0.IDC. Basically it skips the two
> instructions 'DC CVAU' and 'IC IVAU', and the associated loop logic
> in order to avoid the unnecessary overhead.

Cheers, I've queued this for 4.17.

Will