linux-kernel - Re: [PATCH v3 04/24] dmaengine: qcom_hidma: Remove call to memset after dmam_alloc

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Message-ID: <9ea5f97f-5963-5836-6ab2-dc30628c6820@arm.com>
Date:   Tue, 16 Jul 2019 12:35:05 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Sinan Kaya <Okaya@...nel.org>,
        Fuqian Huang <huangfq.daxian@...il.com>
Cc:     Andy Gross <agross@...nel.org>,
        David Brown <david.brown@...aro.org>,
        Vinod Koul <vkoul@...nel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        linux-arm-msm@...r.kernel.org, dmaengine@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH v3 04/24] dmaengine: qcom_hidma: Remove call to memset
 after dmam_alloc_coherent

On 15/07/2019 16:17, Sinan Kaya wrote:
> On 7/15/2019 1:43 AM, Fuqian Huang wrote:
>> Should I rewrite the commit log? Just mention that dma_alloc_coherent
>> has already
>> zeroed the memory and not to reference the commit?
> 
> I'd like to hear from Robin Murphy that arm smmu driver follows this as
> well.

I'd be lying if I said it did.

...but only because that's never been part of the SMMU driver's 
responsibility either way. The iommu-dma layer however, and thus the 
respective arm64 iommu_dma_ops, has always zeroed allocations right from 
its inception.

518a2f1925c3 was just cleaning up the last of the stragglers which 
*weren't* already clearing buffers anyway, such that we could formalise 
that behaviour into the API.

Robin.