linux-kernel - Re: [RFC PATCH v6 1/6] riscv: mm: dma-noncoherent: Switch using function pointers for cache management

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Date:   Tue, 10 Jan 2023 15:11:20 +0000
From:   Will Deacon <will@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Christoph Hellwig <hch@....de>,
        Prabhakar <prabhakar.csengg@...il.com>,
        "Conor.Dooley" <conor.dooley@...rochip.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Heiko Stübner <heiko@...ech.de>,
        guoren <guoren@...nel.org>,
        Andrew Jones <ajones@...tanamicro.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        "open list:RISC-V ARCHITECTURE" <linux-riscv@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "Lad, Prabhakar" <prabhakar.mahadev-lad.rj@...renesas.com>,
        Philipp Tomsich <philipp.tomsich@...ll.eu>,
        Nathan Chancellor <nathan@...nel.org>,
        Atish Patra <atishp@...osinc.com>,
        Anup Patel <apatel@...tanamicro.com>,
        Tsukasa OI <research_trasio@....a4lg.com>,
        Jisheng Zhang <jszhang@...nel.org>,
        Mayuresh Chitale <mchitale@...tanamicro.com>
Subject: Re: [RFC PATCH v6 1/6] riscv: mm: dma-noncoherent: Switch using
 function pointers for cache management

On Tue, Jan 10, 2023 at 04:03:06PM +0100, Arnd Bergmann wrote:
> On Tue, Jan 10, 2023, at 08:01, Christoph Hellwig wrote:
> > On Mon, Jan 09, 2023 at 01:59:12PM +0100, Arnd Bergmann wrote:
> >> I had another look at the arm64 side, which (like the zicbom
> >> variant) uses 'clean' on dma_sync_single_for_device(DMA_FROM_DEVICE),
> >> as that has changed not that long ago, see
> >> 
> >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c50f11c6196f45c92ca48b16a5071615d4ae0572
> >
> > which IIRC has been reverted recently.
> 
> To clarify: I was looking at arch_sync_dma_for_device(), which
> changed from 'invalidate' to 'clean' last June in commit
> c50f11c6196f ("arm64: mm: Don't invalidate FROM_DEVICE buffers
> at start of DMA transfer"). I don't see  a revert for that.
> 
> The one that was reverted recently is arch_dma_prep_coherent, which
> was changed and reverted in
> 
> c44094eee32 Aug 23 2022 flush->clean
> b7d9aae4048 Dec 6  2022 clean->flush
> 
> I'm primarily interested in the streaming mappings (arch_sync_*)
> at the moment.

Just as an FYI, but we plan to revert the revert (i.e. go back to 'clean')
here once Qualcomm's modem firmware loader has been updated:

https://lore.kernel.org/r/20230109034843.23759-1-quic_sibis@quicinc.com

Will