[PATCH v2] dma-contiguous: cleanup dma_alloc_contiguous

[PATCH v2] dma-contiguous: cleanup dma_alloc_contiguous

[Christoph Hellwig]

Split out a cma_alloc_aligned helper to deal with the "interesting"
calling conventions for cma_alloc, which then allows to the main
function to be written straight forward.  This also takes advantage
of the fact that NULL dev arguments have been gone from the DMA API
for a while.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---

Changes since v1:
 - actually pass on the select struct cma
 - clean up cma_alloc_aligned a bit

 kernel/dma/contiguous.c | 31 ++++++++++++++-----------------
 1 file changed, 14 insertions(+), 17 deletions(-)

diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index 15bc5026c485f2..cff7e60968b9e1 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -215,6 +215,13 @@ bool dma_release_from_contiguous(struct device *dev, struct page *pages,
 	return cma_release(dev_get_cma_area(dev), pages, count);
 }
 
+static struct page *cma_alloc_aligned(struct cma *cma, size_t size, gfp_t gfp)
+{
+	unsigned int align = min(get_order(size), CONFIG_CMA_ALIGNMENT);
+
+	return cma_alloc(cma, size >> PAGE_SHIFT, align, gfp & __GFP_NOWARN);
+}
+
 /**
  * dma_alloc_contiguous() - allocate contiguous pages
  * @dev:   Pointer to device for which the allocation is performed.
@@ -231,24 +238,14 @@ bool dma_release_from_contiguous(struct device *dev, struct page *pages,
  */
 struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
 {
-	size_t count = size >> PAGE_SHIFT;
-	struct page *page = NULL;
-	struct cma *cma = NULL;
-
-	if (dev && dev->cma_area)
-		cma = dev->cma_area;
-	else if (count > 1)
-		cma = dma_contiguous_default_area;
-
 	/* CMA can be used only in the context which permits sleeping */
-	if (cma && gfpflags_allow_blocking(gfp)) {
-		size_t align = get_order(size);
-		size_t cma_align = min_t(size_t, align, CONFIG_CMA_ALIGNMENT);
-
-		page = cma_alloc(cma, count, cma_align, gfp & __GFP_NOWARN);
-	}
-
-	return page;
+	if (!gfpflags_allow_blocking(gfp))
+		return NULL;
+	if (dev->cma_area)
+		return cma_alloc_aligned(dev->cma_area, size, gfp);
+	if (size <= PAGE_SIZE || !dma_contiguous_default_area)
+		return NULL;
+	return cma_alloc_aligned(dma_contiguous_default_area, size, gfp);
 }
 
 /**
-- 
2.27.0

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Re: [PATCH v2] dma-contiguous: cleanup dma_alloc_contiguous

[Nicolin Chen]

Hi Christoph,

On Thu, Jul 23, 2020 at 02:01:33PM +0200, Christoph Hellwig wrote:
> Split out a cma_alloc_aligned helper to deal with the "interesting"
> calling conventions for cma_alloc, which then allows to the main
> function to be written straight forward.  This also takes advantage
> of the fact that NULL dev arguments have been gone from the DMA API
> for a while.

I am still seeing some potential NULL dev callers:
drivers/staging/emxx_udc/emxx_udc.c:2596:			ep->virt_buf = dma_alloc_coherent(NULL, PAGE_SIZE,
drivers/tty/synclink.c:3667:		info->buffer_list = dma_alloc_coherent(NULL, BUFFERLISTSIZE, &info->buffer_list_dma_addr, GFP_KERNEL);
drivers/tty/synclink.c:3777:			BufferList[i].virt_addr = dma_alloc_coherent(NULL, DMABUFFERSIZE, &BufferList[i].dma_addr, GFP_KERNEL);

Personally I don't feel that it hurts to check the dev pointer
as we do now, but if you are confident with this version:

Reviewed-by: Nicolin Chen <nicoleotsuka@gmail.com>

Thanks
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RE: [PATCH v2] dma-contiguous: cleanup dma_alloc_contiguous

[Song Bao Hua (Barry Song)]

> -----Original Message-----
> From: iommu [mailto:iommu-bounces@lists.linux-foundation.org] On Behalf
> Of Christoph Hellwig
> Sent: Friday, July 24, 2020 12:02 AM
> To: iommu@lists.linux-foundation.org
> Cc: robin.murphy@arm.com
> Subject: [PATCH v2] dma-contiguous: cleanup dma_alloc_contiguous
> 
> Split out a cma_alloc_aligned helper to deal with the "interesting"
> calling conventions for cma_alloc, which then allows to the main function to
> be written straight forward.  This also takes advantage of the fact that NULL
> dev arguments have been gone from the DMA API for a while.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Reviewed-by: Barry Song <song.bao.hua@hisilicon.com>

And I have rebased per-numa CMA patchset on top of this one.
https://lore.kernel.org/linux-arm-kernel/20200723131344.41472-1-song.bao.hua@hisilicon.com/

> ---
> 
> Changes since v1:
>  - actually pass on the select struct cma
>  - clean up cma_alloc_aligned a bit
> 
>  kernel/dma/contiguous.c | 31 ++++++++++++++-----------------
>  1 file changed, 14 insertions(+), 17 deletions(-)
> 
> diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c index
> 15bc5026c485f2..cff7e60968b9e1 100644
> --- a/kernel/dma/contiguous.c
> +++ b/kernel/dma/contiguous.c
> @@ -215,6 +215,13 @@ bool dma_release_from_contiguous(struct device
> *dev, struct page *pages,
>  	return cma_release(dev_get_cma_area(dev), pages, count);  }
> 
> +static struct page *cma_alloc_aligned(struct cma *cma, size_t size,
> +gfp_t gfp) {
> +	unsigned int align = min(get_order(size), CONFIG_CMA_ALIGNMENT);
> +
> +	return cma_alloc(cma, size >> PAGE_SHIFT, align, gfp & __GFP_NOWARN);
> +}
> +
>  /**
>   * dma_alloc_contiguous() - allocate contiguous pages
>   * @dev:   Pointer to device for which the allocation is performed.
> @@ -231,24 +238,14 @@ bool dma_release_from_contiguous(struct device
> *dev, struct page *pages,
>   */
>  struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
> {
> -	size_t count = size >> PAGE_SHIFT;
> -	struct page *page = NULL;
> -	struct cma *cma = NULL;
> -
> -	if (dev && dev->cma_area)
> -		cma = dev->cma_area;
> -	else if (count > 1)
> -		cma = dma_contiguous_default_area;
> -
>  	/* CMA can be used only in the context which permits sleeping */
> -	if (cma && gfpflags_allow_blocking(gfp)) {
> -		size_t align = get_order(size);
> -		size_t cma_align = min_t(size_t, align, CONFIG_CMA_ALIGNMENT);
> -
> -		page = cma_alloc(cma, count, cma_align, gfp & __GFP_NOWARN);
> -	}
> -
> -	return page;
> +	if (!gfpflags_allow_blocking(gfp))
> +		return NULL;
> +	if (dev->cma_area)
> +		return cma_alloc_aligned(dev->cma_area, size, gfp);
> +	if (size <= PAGE_SIZE || !dma_contiguous_default_area)
> +		return NULL;
> +	return cma_alloc_aligned(dma_contiguous_default_area, size, gfp);
>  }
> 
>  /**
> --
> 2.27.0
Thanks
Barry

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