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 <20230211031821.976408-5-cristian.ciocaltea@collabora.com> <Y+567t+kDjZI+fbo@spud>
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From:   Emil Renner Berthing <emil.renner.berthing@canonical.com>
Date:   Sun, 19 Feb 2023 22:32:52 +0100
Message-ID: <CAJM55Z_poY3dVu9fQ1W1VQw3V=8VdVKc1+qUcdHduM1aAveJUQ@mail.gmail.com>
Subject: Re: [PATCH 04/12] soc: sifive: ccache: Add non-coherent DMA handling
To:     Conor Dooley <conor@kernel.org>
Cc:     Cristian Ciocaltea <cristian.ciocaltea@collabora.com>,
        Lee Jones <lee@kernel.org>, Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Emil Renner Berthing <kernel@esmil.dk>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Giuseppe Cavallaro <peppe.cavallaro@st.com>,
        Alexandre Torgue <alexandre.torgue@foss.st.com>,
        Jose Abreu <joabreu@synopsys.com>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        Richard Cochran <richardcochran@gmail.com>,
        Sagar Kadam <sagar.kadam@sifive.com>,
        Yanhong Wang <yanhong.wang@starfivetech.com>,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, linux-riscv@lists.infradead.org,
        linux-stm32@st-md-mailman.stormreply.com,
        linux-arm-kernel@lists.infradead.org, kernel@collabora.com,
        daire.mcnamara@microchip.com
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On Thu, 16 Feb 2023 at 19:51, Conor Dooley <conor@kernel.org> wrote:
>
> Emil,
>
> +CC Daire
>
> On Sat, Feb 11, 2023 at 05:18:13AM +0200, Cristian Ciocaltea wrote:
> > From: Emil Renner Berthing <kernel@esmil.dk>
> >
> > Add functions to flush the caches and handle non-coherent DMA.
> >
> > Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
> > [replace <asm/cacheflush.h> with <linux/cacheflush.h>]
> > Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
> > ---
>
> > +void *sifive_ccache_set_uncached(void *addr, size_t size)
> > +{
> > +     phys_addr_t phys_addr = __pa(addr) + uncached_offset;
> > +     void *mem_base;
> > +
> > +     mem_base = memremap(phys_addr, size, MEMREMAP_WT);
> > +     if (!mem_base) {
> > +             pr_err("%s memremap failed for addr %p\n", __func__, addr);
> > +             return ERR_PTR(-EINVAL);
> > +     }
> > +
> > +     return mem_base;
> > +}
>
> The rest of this I either get b/c we did it, or will become moot so I
> amn't worried about it, but can you please explain this, in particular
> the memremap that you're doing here?

No, I can't really. As we talked about it's also based on a prototype
by Atish. I'm sure you know that the general idea is that we want to
return a pointer that accesses the same physical memory, but through
the uncached alias. I can't tell you exactly why it's done this way
though, sorry.

/Emil

> Cheers,
> Conor.
>
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