linux-kernel - Re: [PATCH v5 3/7] drivers: dma-coherent: Account dma_pfn

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Date:   Mon, 26 Jun 2017 02:37:51 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Vladimir Murzin <vladimir.murzin@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux@...linux.org.uk, sza@....hu, arnd@...db.de,
        gregkh@...uxfoundation.org, akpm@...ux-foundation.org,
        alexandre.torgue@...com, benjamin.gaignard@...aro.org,
        kbuild-all@...org, Michal Nazarewicz <mina86@...a86.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Roger Quadros <rogerq@...com>
Subject: Re: [PATCH v5 3/7] drivers: dma-coherent: Account dma_pfn_offset
 when used with device tree

On Tue, Jun 20, 2017 at 02:50:34PM +0100, Robin Murphy wrote:
> On 20/06/17 14:42, Christoph Hellwig wrote:
> > Wouldn't the smal patch below solve the same issue in a simple way?
> 
> That assumes that all devices accessing a shared pool will have the same
>  dma_pfn_offset as the first one, which cannot strictly be relied upon
> (even if it is highly likely in practice).

Which seems like another argument why the global pool should be
a different implementation / interface than the per-device dma
mapping helpers..