linux-kernel - Re: [PATCH 08/13] swiotlb-xen: always use dma-direct helpers to alloc coherent pages

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Date:   Tue, 3 Sep 2019 18:15:09 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Christoph Hellwig <hch@....de>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        gross@...e.com
Cc:     x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        xen-devel@...ts.xenproject.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/13] swiotlb-xen: always use dma-direct helpers to alloc
 coherent pages

On 9/2/19 9:03 AM, Christoph Hellwig wrote:
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index b8808677ae1d..f9dd4cb6e4b3 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -299,8 +299,7 @@ xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
>  	 * address. In fact on ARM virt_to_phys only works for kernel direct
>  	 * mapped RAM memory. Also see comment below.
>  	 */
> -	ret = xen_alloc_coherent_pages(hwdev, size, dma_handle, flags, attrs);
> -
> +	ret = dma_direct_alloc(hwdev, size, dma_handle, flags, attrs);


If I am reading __dma_direct_alloc_pages() correctly there is a path
that will force us to use GFP_DMA32 and as Juergen pointed out in
another message that may not be desirable.

-boris