Re: [PATCH 1/2] dma-mapping: fix page attributes for dma_mmap_*

From: Catalin Marinas <catalin.marinas@arm.com>
To: Christoph Hellwig <hch@lst.de>
Cc: iommu@lists.linux-foundation.org,
	Shawn Anastasio <shawn@anastas.io>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Russell King <linux@armlinux.org.uk>,
	Will Deacon <will@kernel.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Paul Burton <paul.burton@mips.com>,
	James Hogan <jhogan@kernel.org>,
	linuxppc-dev@lists.ozlabs.org, linux-mips@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, Gavin Li <git@thegavinli.com>
Subject: Re: [PATCH 1/2] dma-mapping: fix page attributes for dma_mmap_*
Date: Mon, 5 Aug 2019 10:10:52 +0100	[thread overview]
Message-ID: <20190805091051.GB59981@iMac.local> (raw)
In-Reply-To: <20190805080145.5694-2-hch@lst.de>

On Mon, Aug 05, 2019 at 11:01:44AM +0300, Christoph Hellwig wrote:
> All the way back to introducing dma_common_mmap we've defaulyed to mark

s/defaultyed/defaulted/

> the pages as uncached.  But this is wrong for DMA coherent devices.
> Later on DMA_ATTR_WRITE_COMBINE also got incorrect treatment as that
> flag is only treated special on the alloc side for non-coherent devices.
> 
> Introduce a new dma_pgprot helper that deals with the check for coherent
> devices so that only the remapping cases even reach arch_dma_mmap_pgprot

s/even/ever/

> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> index 1d3f0b5a9940..bd2b039f43a6 100644
> --- a/arch/arm64/mm/dma-mapping.c
> +++ b/arch/arm64/mm/dma-mapping.c
> @@ -14,9 +14,7 @@
>  pgprot_t arch_dma_mmap_pgprot(struct device *dev, pgprot_t prot,
>  		unsigned long attrs)
>  {
> -	if (!dev_is_dma_coherent(dev) || (attrs & DMA_ATTR_WRITE_COMBINE))
> -		return pgprot_writecombine(prot);
> -	return prot;
> +	return pgprot_writecombine(prot);
>  }

For arm64:

Acked-by: Catalin Marinas <catalin.marinas@arm.com>