Re: [PATCH v2 04/10] DMA, CMA: support alignment constraint on cma region

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Joonsoo Kim <iamjoonsoo.kim@lge.com> writes:

> ppc kvm's cma area management needs alignment constraint on
> cma region. So support it to prepare generalization of cma area
> management functionality.
>
> Additionally, add some comments which tell us why alignment
> constraint is needed on cma region.
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

>
> diff --git a/drivers/base/dma-contiguous.c b/drivers/base/dma-contiguous.c
> index 8a44c82..bc4c171 100644
> --- a/drivers/base/dma-contiguous.c
> +++ b/drivers/base/dma-contiguous.c
> @@ -32,6 +32,7 @@
>  #include <linux/swap.h>
>  #include <linux/mm_types.h>
>  #include <linux/dma-contiguous.h>
> +#include <linux/log2.h>
>
>  struct cma {
>  	unsigned long	base_pfn;
> @@ -219,6 +220,7 @@ core_initcall(cma_init_reserved_areas);
>   * @size: Size of the reserved area (in bytes),
>   * @base: Base address of the reserved area optional, use 0 for any
>   * @limit: End address of the reserved memory (optional, 0 for any).
> + * @alignment: Alignment for the contiguous memory area, should be power of 2
>   * @res_cma: Pointer to store the created cma region.
>   * @fixed: hint about where to place the reserved area
>   *
> @@ -233,15 +235,15 @@ core_initcall(cma_init_reserved_areas);
>   */
>  static int __init __dma_contiguous_reserve_area(phys_addr_t size,
>  				phys_addr_t base, phys_addr_t limit,
> +				phys_addr_t alignment,
>  				struct cma **res_cma, bool fixed)
>  {
>  	struct cma *cma = &cma_areas[cma_area_count];
> -	phys_addr_t alignment;
>  	int ret = 0;
>
> -	pr_debug("%s(size %lx, base %08lx, limit %08lx)\n", __func__,
> -		 (unsigned long)size, (unsigned long)base,
> -		 (unsigned long)limit);
> +	pr_debug("%s(size %lx, base %08lx, limit %08lx align_order %08lx)\n",
> +		__func__, (unsigned long)size, (unsigned long)base,
> +		(unsigned long)limit, (unsigned long)alignment);
>
>  	/* Sanity checks */
>  	if (cma_area_count = ARRAY_SIZE(cma_areas)) {
> @@ -253,8 +255,17 @@ static int __init __dma_contiguous_reserve_area(phys_addr_t size,
>  	if (!size)
>  		return -EINVAL;
>
> -	/* Sanitise input arguments */
> -	alignment = PAGE_SIZE << max(MAX_ORDER - 1, pageblock_order);
> +	if (alignment && !is_power_of_2(alignment))
> +		return -EINVAL;
> +
> +	/*
> +	 * Sanitise input arguments.
> +	 * CMA area should be at least MAX_ORDER - 1 aligned. Otherwise,
> +	 * CMA area could be merged into other MIGRATE_TYPE by buddy mechanism
> +	 * and CMA property will be broken.
> +	 */
> +	alignment = max(alignment,
> +		(phys_addr_t)PAGE_SIZE << max(MAX_ORDER - 1, pageblock_order));
>  	base = ALIGN(base, alignment);
>  	size = ALIGN(size, alignment);
>  	limit &= ~(alignment - 1);
> @@ -302,7 +313,8 @@ int __init dma_contiguous_reserve_area(phys_addr_t size, phys_addr_t base,
>  {
>  	int ret;
>
> -	ret = __dma_contiguous_reserve_area(size, base, limit, res_cma, fixed);
> +	ret = __dma_contiguous_reserve_area(size, base, limit, 0,
> +						res_cma, fixed);
>  	if (ret)
>  		return ret;
>
> -- 
> 1.7.9.5