Re: [PATCH] dma-pool: Do not allocate pool memory from CMA

[Amit Pundir <amit.pundir@linaro.org>]

On Fri, 24 Jul 2020 at 19:11, Christoph Hellwig <hch@lst.de> wrote:
>
> Yes, the iommu is an interesting case, and the current code is
> wrong for that.  Can you try the patch below?  It contains a modified
> version of Nicolas' patch to try CMA again for the expansion and a new
> (for now hackish) way to not apply the addressability check for dma-iommu
> allocations.

Thank you. The below patch worked on today's linux/master (f37e99aca03f).

Regards,
Amit Pundir

>
> diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
> index 6bc74a2d51273e..ec5e525d2b9309 100644
> --- a/kernel/dma/pool.c
> +++ b/kernel/dma/pool.c
> @@ -3,7 +3,9 @@
>   * Copyright (C) 2012 ARM Ltd.
>   * Copyright (C) 2020 Google LLC
>   */
> +#include <linux/cma.h>
>  #include <linux/debugfs.h>
> +#include <linux/dma-contiguous.h>
>  #include <linux/dma-direct.h>
>  #include <linux/dma-noncoherent.h>
>  #include <linux/init.h>
> @@ -55,6 +57,31 @@ static void dma_atomic_pool_size_add(gfp_t gfp, size_t size)
>                 pool_size_kernel += size;
>  }
>
> +static bool cma_in_zone(gfp_t gfp)
> +{
> +       phys_addr_t end;
> +       unsigned long size;
> +       struct cma *cma;
> +
> +       cma = dev_get_cma_area(NULL);
> +       if (!cma)
> +               return false;
> +
> +       size = cma_get_size(cma);
> +       if (!size)
> +               return false;
> +       end = cma_get_base(cma) - memblock_start_of_DRAM() + size - 1;
> +
> +       /* CMA can't cross zone boundaries, see cma_activate_area() */
> +       if (IS_ENABLED(CONFIG_ZONE_DMA) && (gfp & GFP_DMA) &&
> +           end <= DMA_BIT_MASK(zone_dma_bits))
> +               return true;
> +       if (IS_ENABLED(CONFIG_ZONE_DMA32) && (gfp & GFP_DMA32) &&
> +           end <= DMA_BIT_MASK(32))
> +               return true;
> +       return true;
> +}
> +
>  static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
>                               gfp_t gfp)
>  {
> @@ -68,7 +95,11 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
>
>         do {
>                 pool_size = 1 << (PAGE_SHIFT + order);
> -               page = alloc_pages(gfp, order);
> +               if (cma_in_zone(gfp))
> +                       page = dma_alloc_from_contiguous(NULL, 1 << order,
> +                                                        order, false);
> +               if (!page)
> +                       page = alloc_pages(gfp, order);
>         } while (!page && order-- > 0);
>         if (!page)
>                 goto out;
> @@ -251,7 +282,11 @@ void *dma_alloc_from_pool(struct device *dev, size_t size,
>                         continue;
>
>                 phys = gen_pool_virt_to_phys(pool, val);
> -               if (dma_coherent_ok(dev, phys, size))
> +               /*
> +                * Only apply the addressability check for dma-direct.
> +                * This is a nasty hack and won't work e.g. for arm.
> +                */
> +               if (get_dma_ops(dev) || dma_coherent_ok(dev, phys, size))
>                         break;
>
>                 gen_pool_free(pool, val, size);
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