linux-kernel - Re: [RFCv3][PATCH 3/5] arm64: Implement ARCH_HAS_FORCE

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Message-ID: <20160913151325.GF17731@arm.com>
Date:   Tue, 13 Sep 2016 16:14:03 +0100
From:   Will Deacon <will.deacon@....com>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Sumit Semwal <sumit.semwal@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Riley Andrews <riandrews@...roid.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        linaro-mm-sig@...ts.linaro.org, devel@...verdev.osuosl.org,
        Russell King <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Eun Taik Lee <eun.taik.lee@...sung.com>,
        Rohit kumar <rohit.kr@...sung.com>,
        Liviu Dudau <Liviu.Dudau@....com>,
        Jon Medhurst <tixy@...aro.org>,
        Jeremy Gebben <jgebben@...eaurora.org>,
        Bryan Huntsman <bryanh@...eaurora.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [RFCv3][PATCH 3/5] arm64: Implement ARCH_HAS_FORCE_CACHE

On Tue, Sep 13, 2016 at 08:02:20AM -0700, Laura Abbott wrote:
> On 09/13/2016 02:19 AM, Will Deacon wrote:
> >On Mon, Sep 12, 2016 at 02:32:56PM -0700, Laura Abbott wrote:
> >>
> >>arm64 may need to guarantee the caches are synced. Implement versions of
> >>the kernel_force_cache API to allow this.
> >>
> >>Signed-off-by: Laura Abbott <labbott@...hat.com>
> >>---
> >>v3: Switch to calling cache operations directly instead of relying on
> >>DMA mapping.
> >>---
> >> arch/arm64/include/asm/cacheflush.h |  8 ++++++++
> >> arch/arm64/mm/cache.S               | 24 ++++++++++++++++++++----
> >> arch/arm64/mm/flush.c               | 11 +++++++++++
> >> 3 files changed, 39 insertions(+), 4 deletions(-)
> >
> >I'm really hesitant to expose these cache routines as an API solely to
> >support a driver sitting in staging/. I appreciate that there's a chicken
> >and egg problem here, but we *really* don't want people using these routines
> >in preference to the DMA API, and I fear that we'll simply grow a bunch
> >more users of these things if we promote it as an API like you're proposing.
> >
> >Can the code not be contained under staging/, as part of ion?
> >
> 
> I proposed that in V1 and it was suggested I make it a proper API
> 
> http://www.mail-archive.com/driverdev-devel@linuxdriverproject.org/msg47654.html
> http://www.mail-archive.com/driverdev-devel@linuxdriverproject.org/msg47672.html

:/ then I guess we're in disagreement. If ion really needs this stuff
(which I don't fully grok), perhaps we should be exposing something at
a higher level from the architecture, so it really can't be used for
anything other than ion.

Will