linux-kernel - Re: [RFC PATCH 1/4] dma-mapping: Generalise dma_32bit

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Date:   Tue, 10 Jul 2018 20:04:33 +0200
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     hch@....de, m.szyprowski@...sung.com,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        lorenzo.pieralisi@....com, hanjun.guo@...aro.org,
        sudeep.holla@....com, robh+dt@...nel.org, frowand.list@...il.com,
        gregkh@...uxfoundation.org, joro@...tes.org, x86@...nel.org
Subject: Re: [RFC PATCH 1/4] dma-mapping: Generalise dma_32bit_limit flag

On Tue, Jul 10, 2018 at 06:17:16PM +0100, Robin Murphy wrote:
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 8be8106270c2..95e185347e34 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -183,7 +183,7 @@ int dma_direct_supported(struct device *dev, u64 mask)
>  	 * Various PCI/PCIe bridges have broken support for > 32bit DMA even
>  	 * if the device itself might support it.
>  	 */
> -	if (dev->dma_32bit_limit && mask > DMA_BIT_MASK(32))
> +	if (dev->bus_dma_mask && mask > dev->bus_dma_mask)
>  		return 0;

The comment above this check needs an updated (or just be removed).

Also we still have a few architectures not using dma-direct. I guess
most were doing fine without such limits anyway, but at least arm
will probably need an equivalent check.