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From:   Vineet Gupta <vineet.gupta1@synopsys.com>
To:     Jose Abreu <jose.abreu@synopsys.com>,
        "linux-snps-arc@lists.infradead.org" 
        <linux-snps-arc@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Alexey Brodkin <alexey.brodkin@synopsys.com>,
        Joao Pinto <joao.pinto@synopsys.com>,
        Vitor Soares <vitor.soares@synopsys.com>,
        David Laight <David.Laight@ACULAB.COM>
Subject: Re: [PATCH v3] ARC: io.h: Implement reads{x}()/writes{x}()
Thread-Topic: [PATCH v3] ARC: io.h: Implement reads{x}()/writes{x}()
Thread-Index: AQHUiJG/o7fyzIGCckGLnUFm4swJ4g==
Date:   Fri, 30 Nov 2018 19:29:44 +0000
Message-ID: <C2D7FE5348E1B147BCA15975FBA23075014641A449@US01WEMBX2.internal.synopsys.com>
References: <244eba764469e8493f2d0c85a6d965aad6cd8128.1543571088.git.joabreu@synopsys.com>
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On 11/30/18 1:47 AM, Jose Abreu wrote:=0A=
> Some ARC CPU's do not support unaligned loads/stores. Currently, generic=
=0A=
> implementation of reads{b/w/l}()/writes{b/w/l}() is being used with ARC.=
=0A=
> This can lead to misfunction of some drivers as generic functions do a=0A=
> plain dereference of a pointer that can be unaligned.=0A=
>=0A=
> Let's use {get/put}_unaligned() helpers instead of plain dereference of=
=0A=
> pointer in order to fix. The helpers allow to get and store data from an=
=0A=
> unaligned address whilst preserving the CPU internal alignment.=0A=
> According to [1], the use of these helpers are costly in terms of=0A=
> performance so we added an initial check for a buffer already aligned so=
=0A=
> that the usage of the helpers can be avoided, when possible.=0A=
>=0A=
> [1] Documentation/unaligned-memory-access.txt=0A=
>=0A=
> Changes from v2:=0A=
> - Rework commit msg (Vineet)=0A=
> - Check if count is 0 and return (Vineet)=0A=
> - Use two different loops (Vineet)=0A=
>=0A=
> Changes from v1:=0A=
> - Check if buffer is already aligned (David)=0A=
> - Remove 64 bit mention (Alexey)=0A=
>=0A=
> Signed-off-by: Jose Abreu <joabreu@synopsys.com>=0A=
> Tested-by: Vitor Soares <soares@synopsys.com>=0A=
> Cc: Vineet Gupta <vgupta@synopsys.com>=0A=
> Cc: Alexey Brodkin <abrodkin@synopsys.com>=0A=
> Cc: Joao Pinto <jpinto@synopsys.com>=0A=
> Cc: Vitor Soares <soares@synopsys.com>=0A=
> Cc: David Laight <David.Laight@ACULAB.COM>=0A=
=0A=
Applied to for-curr after some minor chg (added a comment about accessor)=
=0A=
=0A=
Thx,=0A=
-Vineet=0A=