netdev - Re: [net-next PATCH V2 1/3] mm: add dma_addr

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Message-ID: <2d0de75d-960c-6866-b396-86490ca479af@gmail.com>
Date:   Tue, 12 Feb 2019 10:23:52 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
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>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        mgorman@...hsingularity.net,
        "David S. Miller" <davem@...emloft.net>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [net-next PATCH V2 1/3] mm: add dma_addr_t to struct page

On 2/12/19 10:19 AM, Jesper Dangaard Brouer wrote:
> On Tue, 12 Feb 2019 10:05:39 -0800
> Florian Fainelli <f.fainelli@...il.com> wrote:
> 
>> On 2/12/19 6:49 AM, Jesper Dangaard Brouer 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
>>>
>>> Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
>>> Signed-off-by: Ilias Apalodimas <ilias.apalodimas@...aro.org>
>>> Acked-by: Andrew Morton <akpm@...ux-foundation.org>
>>> ---
>>>  include/linux/mm_types.h |    7 +++++++
>>>  1 file changed, 7 insertions(+)
>>>
>>> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
>>> index 2c471a2c43fa..581737bd0878 100644
>>> --- a/include/linux/mm_types.h
>>> +++ b/include/linux/mm_types.h
>>> @@ -95,6 +95,13 @@ struct page {
>>>  			 */
>>>  			unsigned long private;
>>>  		};
>>> +		struct {	/* page_pool used by netstack */
>>> +			/**
>>> +			 * @dma_addr: page_pool requires a 64-bit value even on
>>> +			 * 32-bit architectures.
>>> +			 */  
>>
>> Nit: might require? dma_addr_t, as you mention in the commit may have a
>> different size based on CONFIG_ARCH_DMA_ADDR_T_64BIT.
> 
> So you want me to change the comment to be:
> 
> /**
>  * @dma_addr: might require a 64-bit value even on
>  * 32-bit architectures.
>  */
> 
> Correctly understood?

Correct, that is what I would change. The commit message is correct, but
the comment makes it sound like dma_addr_t is guaranteed to be 64-bit,
while it is actually platform dependent. Does that make it clearer?
-- 
Florian