linux-kernel - Re: [RFC PATCH] dma: coherent: respect to device 'dma-coherent' property

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Message-ID: <20230416063028.GA6276@lst.de>
Date:   Sun, 16 Apr 2023 08:30:28 +0200
From:   Christoph Hellwig <hch@....de>
To:     Zhiqiang Hou <Zhiqiang.Hou@....com>
Cc:     iommu@...ts.linux.dev, linux-kernel@...r.kernel.org, hch@....de,
        m.szyprowski@...sung.com, robin.murphy@....com
Subject: Re: [RFC PATCH] dma: coherent: respect to device 'dma-coherent'
 property

On Fri, Apr 14, 2023 at 04:03:07PM +0800, Zhiqiang Hou wrote:
> From: Hou Zhiqiang <Zhiqiang.Hou@....com>
> 
> Currently, the coherent DMA memory is always mapped as writecombine
> and uncached, ignored the 'dma-coherent' property in device node,
> this patch is to map the memory as writeback and cached when the
> device has 'dma-coherent' property.

What is the use case here?  The somewhat misnamed per-device coherent
memory is intended for small per-device pools of sram or such
used for staging memory.