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Message-ID: <CAJM55Z_poY3dVu9fQ1W1VQw3V=8VdVKc1+qUcdHduM1aAveJUQ@mail.gmail.com>
Date: Sun, 19 Feb 2023 22:32:52 +0100
From: Emil Renner Berthing <emil.renner.berthing@...onical.com>
To: Conor Dooley <conor@...nel.org>
Cc: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>,
Lee Jones <lee@...nel.org>, Rob Herring <robh+dt@...nel.org>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Emil Renner Berthing <kernel@...il.dk>,
Palmer Dabbelt <palmer@...belt.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Albert Ou <aou@...s.berkeley.edu>,
Giuseppe Cavallaro <peppe.cavallaro@...com>,
Alexandre Torgue <alexandre.torgue@...s.st.com>,
Jose Abreu <joabreu@...opsys.com>,
Maxime Coquelin <mcoquelin.stm32@...il.com>,
Richard Cochran <richardcochran@...il.com>,
Sagar Kadam <sagar.kadam@...ive.com>,
Yanhong Wang <yanhong.wang@...rfivetech.com>,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
netdev@...r.kernel.org, linux-riscv@...ts.infradead.org,
linux-stm32@...md-mailman.stormreply.com,
linux-arm-kernel@...ts.infradead.org, kernel@...labora.com,
daire.mcnamara@...rochip.com
Subject: Re: [PATCH 04/12] soc: sifive: ccache: Add non-coherent DMA handling
On Thu, 16 Feb 2023 at 19:51, Conor Dooley <conor@...nel.org> wrote:
>
> Emil,
>
> +CC Daire
>
> On Sat, Feb 11, 2023 at 05:18:13AM +0200, Cristian Ciocaltea wrote:
> > From: Emil Renner Berthing <kernel@...il.dk>
> >
> > Add functions to flush the caches and handle non-coherent DMA.
> >
> > Signed-off-by: Emil Renner Berthing <kernel@...il.dk>
> > [replace <asm/cacheflush.h> with <linux/cacheflush.h>]
> > Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@...labora.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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