linux-kernel - Re: [PATCH net-next v3 1/4] page_pool: frag API support for 32-bit arch with 64-bit DMA

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Message-ID: <4f1a0b7d-973f-80f5-cc39-74f09622ccef@redhat.com>
Date:   Fri, 9 Jun 2023 17:02:54 +0200
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     Yunsheng Lin <linyunsheng@...wei.com>, davem@...emloft.net,
        kuba@...nel.org, pabeni@...hat.com
Cc:     brouer@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        linux-rdma@...r.kernel.org
Subject: Re: [PATCH net-next v3 1/4] page_pool: frag API support for 32-bit
 arch with 64-bit DMA


On 09/06/2023 15.17, Yunsheng Lin wrote:
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> index a7c526ee5024..cd4ac378cc63 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> @@ -832,6 +832,15 @@ static int mlx5e_alloc_rq(struct mlx5e_params *params,
>   		/* Create a page_pool and register it with rxq */
>   		struct page_pool_params pp_params = { 0 };
>   
> +		/* Return error here to aoivd writing to page->pp_frag_count in
                                         ^^^^^
Typo

> +		 * mlx5e_page_release_fragmented() for page->pp_frag_count is not
> +		 * usable for arch with PAGE_POOL_DMA_USE_PP_FRAG_COUNT being true.
> +		 */
> +		if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT) {
> +			err = -EINVAL;
> +			goto err_free_by_rq_type;
> +		}
> +
>   		pp_params.order     = 0;
>   		pp_params.flags     = PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV | PP_FLAG_PAGE_FRAG;
>   		pp_params.pool_size = pool_size;
> diff --git a/include/net/page_pool.h b/include/net/page_pool.h
> index 126f9e294389..5c7f7501f300 100644
> --- a/include/net/page_pool.h
> +++ b/include/net/page_pool.h
> @@ -33,6 +33,7 @@
>   #include <linux/mm.h> /* Needed by ptr_ring */
>   #include <linux/ptr_ring.h>
>   #include <linux/dma-direction.h>
> +#include <linux/dma-mapping.h>
>   
>   #define PP_FLAG_DMA_MAP		BIT(0) /* Should page_pool do the DMA
>   					* map/unmap
> @@ -50,6 +51,9 @@
>   				 PP_FLAG_DMA_SYNC_DEV |\
>   				 PP_FLAG_PAGE_FRAG)
>   
> +#define PAGE_POOL_DMA_USE_PP_FRAG_COUNT	\
> +		(sizeof(dma_addr_t) > sizeof(unsigned long))
> +

I have a problem with the name PAGE_POOL_DMA_USE_PP_FRAG_COUNT
because it is confusing to read in an if-statement.

Proposals rename to:  DMA_OVERLAP_PP_FRAG_COUNT
  Or:  MM_DMA_OVERLAP_PP_FRAG_COUNT
  Or:  DMA_ADDR_OVERLAP_PP_FRAG_COUNT

Notice how I also removed the prefix PAGE_POOL_ because this is a 
MM-layer constraint and not a property of page_pool.


--Jesper