netdev - Re: [net-next PATCH 1/2] mm: add dma_addr

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Message-Id: <20190211121624.30c601d0fa4c0f972eeaf1c6@linux-foundation.org>
Date:   Mon, 11 Feb 2019 12:16:24 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     netdev@...r.kernel.org, linux-mm@...ck.org,
        Toke Høiland-Jørgensen 
        <toke@...e.dk>, Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        willy@...radead.org, Saeed Mahameed <saeedm@...lanox.com>,
        mgorman@...hsingularity.net,
        "David S. Miller" <davem@...emloft.net>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [net-next PATCH 1/2] mm: add dma_addr_t to struct page

On Mon, 11 Feb 2019 17:06:46 +0100 Jesper Dangaard Brouer <brouer@...hat.com> wrote:

> The page_pool API is using page->private to store DMA addresses.
> As pointed out by David Miller we can't use that on 32-bit architectures
> with 64-bit DMA
> 
> This patch adds a new dma_addr_t struct to allow storing DMA addresses
> 
> ..
>
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -95,6 +95,14 @@ struct page {
>  			 */
>  			unsigned long private;
>  		};
> +		struct {	/* page_pool used by netstack */
> +			/**
> +			 * @dma_addr: Page_pool need to store DMA-addr, and
> +			 * cannot use @private, as DMA-mappings can be 64-bit
> +			 * even on 32-bit Architectures.
> +			 */

This comment is a bit awkward.  The discussion about why it doesn't use
->private is uninteresting going forward and is more material for a
changelog.

How about

			/**
			 * @dma_addr: page_pool requires a 64-bit value even on
			 * 32-bit architectures.
			 */

Otherwise,

Acked-by: Andrew Morton <akpm@...ux-foundation.org>