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

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Date:   Fri, 6 Jan 2023 23:29:21 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     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 Fri, Jan 06, 2023 at 11:31:33PM +0100, Arnd Bergmann wrote:
> On Fri, Jan 6, 2023, at 19:55, Prabhakar wrote:
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > +struct riscv_cache_ops zicbom_cmo_ops = {
> > +	.clean_range = &zicbom_cmo_clean_range,
> > +	.inv_range = &zicbom_cmo_inval_range,
> > +	.flush_range = &zicbom_cmo_flush_range,
> > +};
> > +#else
> > +struct riscv_cache_ops zicbom_cmo_ops = {
> > +	.clean_range = NULL,
> > +	.inv_range = NULL,
> > +	.flush_range = NULL,
> > +	.riscv_dma_noncoherent_cmo_ops = NULL,
> > +};
> > +#endif
> > +EXPORT_SYMBOL(zicbom_cmo_ops);
> 
> Same here: If the ZICBOM ISA is disabled, nothing should
> reference zicbom_cmo_ops.

> Also, since ZICBOM is a standard
> extension, I think it makes sense to always have it enabled,
> at least whenever noncoherent DMA is supported, that way
> it can be the default that gets used in the absence of any
> nonstandard cache controller.

While I think of it, this is not possible as Zicbom requires toolchain
support whereas the alternative methods for non-coherent DMA do not.

Thanks,
Conor.


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