linux-kernel - Re: [PATCH 13/21] arc: dma-mapping: skip invalidating before bidirectional DMA

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Message-ID: <2b298e8c-e6fc-a973-9f42-b6a88e92838a@kernel.org>
Date:   Sun, 2 Apr 2023 12:22:20 +0530
From:   Vineet Gupta <vgupta@...nel.org>
To:     Arnd Bergmann <arnd@...nel.org>, linux-kernel@...r.kernel.org
Cc:     Arnd Bergmann <arnd@...db.de>, Vineet Gupta <vgupta@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Guo Ren <guoren@...nel.org>,
        Brian Cain <bcain@...cinc.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Michal Simek <monstr@...str.eu>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Stafford Horne <shorne@...il.com>,
        Helge Deller <deller@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Rich Felker <dalias@...c.org>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        "David S. Miller" <davem@...emloft.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        Christoph Hellwig <hch@....de>,
        Robin Murphy <robin.murphy@....com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        linux-snps-arc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-oxnas@...ups.io,
        linux-csky@...r.kernel.org, linux-hexagon@...r.kernel.org,
        linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
        linux-openrisc@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-xtensa@...ux-xtensa.org,
        Shahab Vahedi <Shahab.Vahedi@...opsys.com>
Subject: Re: [PATCH 13/21] arc: dma-mapping: skip invalidating before
 bidirectional DMA

CC Shahab

On 3/27/23 17:43, Arnd Bergmann wrote:
> From: Arnd Bergmann<arnd@...db.de>
>
> Some architectures that need to invalidate buffers after bidirectional
> DMA because of speculative prefetching only do a simpler writeback
> before that DMA, while architectures that don't need to do the second
> invalidate tend to have a combined writeback+invalidate before the
> DMA.
>
> arc is one of the architectures that does both, which seems unnecessary.
>
> Change it to behave like arm/arm64/xtensa instead, and use just a
> writeback before the DMA when we do the invalidate afterwards.
>
> Signed-off-by: Arnd Bergmann<arnd@...db.de>

Reviewed-by: Vineet Gupta <vgupta@...nel.org>

Shahab can you give this a spin on hsdk - run glibc testsuite over ssh 
and make sure nothing strange happens.

Thx,
-Vineet