Re: [RFC PATCH 2/4] dma/pool: Add an API to check if DMA allocation is from pool

[Pranjal Shrivastava <praan@google.com>]

On Tue, May 05, 2026 at 12:27:35AM +0000, Samiullah Khawaja wrote:
> DMA allocations can be done through DMA pools, add an API that can be
> used to check if an allocation is done from a pool. This will be used in
> the later commit during preservation of DMA allocation.
> 
> Signed-off-by: Samiullah Khawaja <skhawaja@google.com>
> ---
>  include/linux/dma-map-ops.h |  1 +
>  kernel/dma/pool.c           | 13 +++++++++++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
> index 6a1832a73cad..6a0bc4ea2467 100644
> --- a/include/linux/dma-map-ops.h
> +++ b/include/linux/dma-map-ops.h
> @@ -216,6 +216,7 @@ struct page *dma_alloc_from_pool(struct device *dev, size_t size,
>  		bool (*phys_addr_ok)(struct device *, phys_addr_t, size_t));
>  bool dma_free_from_pool(struct device *dev, void *start, size_t size);
>  
> +bool dma_is_from_pool(struct device *dev, void *start, size_t size);
>  int dma_direct_set_offset(struct device *dev, phys_addr_t cpu_start,
>  		dma_addr_t dma_start, u64 size);
>  
> diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
> index 2b2fbb709242..32ce4d6d7683 100644
> --- a/kernel/dma/pool.c
> +++ b/kernel/dma/pool.c
> @@ -307,3 +307,16 @@ bool dma_free_from_pool(struct device *dev, void *start, size_t size)
>  
>  	return false;
>  }
> +
> +bool dma_is_from_pool(struct device *dev, void *start, size_t size)

Do we need struct device here? It seems unused?

Nit: we only ever pass 0 gfp_flags to dma_guess_pool, should we instead
name it: dma_is_from_atomic_pool() to be more accurate?

> +{
> +	struct gen_pool *pool = NULL;
> +
> +	while ((pool = dma_guess_pool(pool, 0))) {
> +		if (!gen_pool_has_addr(pool, (unsigned long)start, size))
> +			continue;
> +		return true;
> +	}

Nit: The loop looks slightly ugly, can we have:

struct gen_pool *pool;

for (pool = dma_guess_pool(NULL, 0); pool != NULL; pool = dma_guess_pool(pool, 0)) {
	if (gen_pool_has_addr(pool, (unsigned long)start, size))
		return true;
}

> +
> +	return false;
> +}
> -- 
> 2.54.0.545.g6539524ca2-goog
> 

Thanks,
Praan