linux-kernel - Re: [PATCH 06/11] swiotlb-xen: always use dma-direct helpers to alloc coherent pages

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Date:   Thu, 29 Aug 2019 15:46:53 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Christoph Hellwig <hch@....de>
cc:     Stefano Stabellini <sstabellini@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        xen-devel@...ts.xenproject.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, jgross@...e.com,
        boris.ostrovsky@...cle.com
Subject: Re: [PATCH 06/11] swiotlb-xen: always use dma-direct helpers to
 alloc coherent pages

+ Boris, Juergen

On Mon, 26 Aug 2019, Christoph Hellwig wrote:
> x86 currently calls alloc_pages, but using dma-direct works as well
> there, with the added benefit of using the CMA pool if available.
> The biggest advantage is of course to remove a pointless bit of
> architecture specific code.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  arch/x86/include/asm/xen/page-coherent.h | 16 ----------------
>  drivers/xen/swiotlb-xen.c                |  7 +++----
>  include/xen/arm/page-coherent.h          | 12 ------------
>  3 files changed, 3 insertions(+), 32 deletions(-)
> 
> diff --git a/arch/x86/include/asm/xen/page-coherent.h b/arch/x86/include/asm/xen/page-coherent.h
> index 116777e7f387..8ee33c5edded 100644
> --- a/arch/x86/include/asm/xen/page-coherent.h
> +++ b/arch/x86/include/asm/xen/page-coherent.h
> @@ -5,22 +5,6 @@
>  #include <asm/page.h>
>  #include <linux/dma-mapping.h>
>  
> -static inline void *xen_alloc_coherent_pages(struct device *hwdev, size_t size,
> -		dma_addr_t *dma_handle, gfp_t flags,
> -		unsigned long attrs)
> -{
> -	void *vstart = (void*)__get_free_pages(flags, get_order(size));
> -	*dma_handle = virt_to_phys(vstart);

This is where we need Boris and Juergen's opinion. From an ARM POV it
looks OK.


> -	return vstart;
> -}
> -
> -static inline void xen_free_coherent_pages(struct device *hwdev, size_t size,
> -		void *cpu_addr, dma_addr_t dma_handle,
> -		unsigned long attrs)
> -{
> -	free_pages((unsigned long) cpu_addr, get_order(size));
> -}
> -
>  static inline void xen_dma_map_page(struct device *hwdev, struct page *page,
>  	     dma_addr_t dev_addr, unsigned long offset, size_t size,
>  	     enum dma_data_direction dir, unsigned long attrs) { }
> 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 (!ret)
>  		return ret;
>  
> @@ -319,7 +318,7 @@ xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
>  	else {
>  		if (xen_create_contiguous_region(phys, order,
>  						 fls64(dma_mask), dma_handle) != 0) {
> -			xen_free_coherent_pages(hwdev, size, ret, (dma_addr_t)phys, attrs);
> +			dma_direct_free(hwdev, size, ret, (dma_addr_t)phys, attrs);
>  			return NULL;
>  		}
>  		SetPageXenRemapped(virt_to_page(ret));
> @@ -351,7 +350,7 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
>  	    TestClearPageXenRemapped(virt_to_page(vaddr)))
>  		xen_destroy_contiguous_region(phys, order);
>  
> -	xen_free_coherent_pages(hwdev, size, vaddr, (dma_addr_t)phys, attrs);
> +	dma_direct_free(hwdev, size, vaddr, (dma_addr_t)phys, attrs);
>  }
>  
>  /*
> diff --git a/include/xen/arm/page-coherent.h b/include/xen/arm/page-coherent.h
> index a840d6949a87..0e244f4fec1a 100644
> --- a/include/xen/arm/page-coherent.h
> +++ b/include/xen/arm/page-coherent.h
> @@ -16,18 +16,6 @@ void __xen_dma_sync_single_for_cpu(struct device *hwdev,
>  void __xen_dma_sync_single_for_device(struct device *hwdev,
>  		dma_addr_t handle, size_t size, enum dma_data_direction dir);
>  
> -static inline void *xen_alloc_coherent_pages(struct device *hwdev, size_t size,
> -		dma_addr_t *dma_handle, gfp_t flags, unsigned long attrs)
> -{
> -	return dma_direct_alloc(hwdev, size, dma_handle, flags, attrs);
> -}
> -
> -static inline void xen_free_coherent_pages(struct device *hwdev, size_t size,
> -		void *cpu_addr, dma_addr_t dma_handle, unsigned long attrs)
> -{
> -	dma_direct_free(hwdev, size, cpu_addr, dma_handle, attrs);
> -}
> -
>  static inline void xen_dma_sync_single_for_cpu(struct device *hwdev,
>  		dma_addr_t handle, size_t size, enum dma_data_direction dir)
>  {
> -- 
> 2.20.1
>