netdev - Re: [PATCH 3/4] net: qcom/emac: enforce DMA address restrictions

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Message-ID: <e523734d-d845-8eae-4a5b-e679b8e46654@codeaurora.org>
Date:   Thu, 12 Oct 2017 09:13:25 -0500
From:   Timur Tabi <timur@...eaurora.org>
To:     David Laight <David.Laight@...LAB.COM>,
        "David S. Miller" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 3/4] net: qcom/emac: enforce DMA address restrictions

On 10/12/17 4:30 AM, David Laight wrote:
> Isn't the memory allocated by a single kzalloc() call?

dma_alloc_coherenent, actually.

> IIRC that guarantees it doesn't cross a power or 2 boundary less than
> the size.

I'm pretty sure that kzalloc does not make that guarantee, and I don't 
think dma_alloc_coherent does either.

> So if you allocate any size between 4k and 8k it won't cross an odd
> 4k boundary (etc).
> 
> So these checks are entirely pointless.

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