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

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Message-ID: <20190212092846.109c9bdf@carbon>
Date:   Tue, 12 Feb 2019 09:28:46 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
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>, brouer@...hat.com
Subject: Re: [net-next PATCH 1/2] mm: add dma_addr_t to struct page

On Mon, 11 Feb 2019 12:16:24 -0800
Andrew Morton <akpm@...ux-foundation.org> wrote:

> 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.
> 			 */

Much better, I'll use that!

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

Thanks!

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer