Date:   Mon, 13 Feb 2023 22:12:57 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     Herbert Xu <herbert@gondor.apana.org.au>
Cc:     JiaJie Ho <jiajie.ho@starfivetech.com>,
        "David S . Miller" <davem@davemloft.net>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Emil Renner Berthing <kernel@esmil.dk>,
        Conor Dooley <conor.dooley@microchip.com>,
        "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-riscv@lists.infradead.org" <linux-riscv@lists.infradead.org>
Subject: Re: [PATCH v2 4/4] crypto: starfive - Add hash and HMAC support
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References: <20230130154242.112613-1-jiajie.ho@starfivetech.com>
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On Thu, Feb 09, 2023 at 05:43:34PM +0800, Herbert Xu wrote:
> On Thu, Feb 09, 2023 at 09:33:06AM +0000, JiaJie Ho wrote:
> >
> > The DMA can only support 32-bit addressing.
> > So, I am copying everything in case kernel allocated memory region >32-bit for a user app.
> 
> Does your hardware support scatter-and-gather? If so you should
> at least allocate individual pages rather than one contiguous buffer.
> 
> Then you can allocate them on-demand rather than before-hand.
> 
> It would also be nice to not do the copy if the input you were
> given was in low memory (and contiguous if your hardware doesn't
> do SG).

All of that is done by the DMA API, or more specifically swiotlb and
does not need to be duplicated in individual drivers.