linux-kernel - Re: [PATCH net-next 1/7] page_pool: disable dma mapping support for 32-bit arch with 64-bit DMA

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Date:   Thu, 23 Sep 2021 19:13:11 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Jesper Dangaard Brouer <jbrouer@...hat.com>
CC:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Networking <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        <linuxarm@...neuler.org>, Jesper Dangaard Brouer <hawk@...nel.org>,
        "Jonathan Lemon" <jonathan.lemon@...il.com>,
        Alexander Lobakin <alobakin@...me>,
        "Willem de Bruijn" <willemb@...gle.com>,
        Cong Wang <cong.wang@...edance.com>,
        "Paolo Abeni" <pabeni@...hat.com>, Kevin Hao <haokexin@...il.com>,
        Aleksandr Nogikh <nogikh@...gle.com>,
        Marco Elver <elver@...gle.com>, <memxor@...il.com>,
        "Eric Dumazet" <edumazet@...gle.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        David Ahern <dsahern@...il.com>
Subject: Re: [PATCH net-next 1/7] page_pool: disable dma mapping support for
 32-bit arch with 64-bit DMA

On 2021/9/23 18:02, Ilias Apalodimas wrote:
> Hi Jesper,
> 
> On Thu, 23 Sept 2021 at 12:33, Jesper Dangaard Brouer
> <jbrouer@...hat.com> wrote:
>>
>>
>> On 22/09/2021 11.41, Yunsheng Lin wrote:
>>> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
>>> index 1a6978427d6c..a65bd7972e37 100644
>>> --- a/net/core/page_pool.c
>>> +++ b/net/core/page_pool.c
>>> @@ -49,6 +49,12 @@ static int page_pool_init(struct page_pool *pool,
>>>        * which is the XDP_TX use-case.
>>>        */
>>>       if (pool->p.flags & PP_FLAG_DMA_MAP) {
>>> +             /* DMA-mapping is not supported on 32-bit systems with
>>> +              * 64-bit DMA mapping.
>>> +              */
>>> +             if (sizeof(dma_addr_t) > sizeof(unsigned long))
>>> +                     return -EINVAL;
>>
>> As I said before, can we please use another error than EINVAL.
>> We should give drivers a chance/ability to detect this error, and e.g.
>> fallback to doing DMA mappings inside driver instead.
>>
>> I suggest using EOPNOTSUPP 95 (Operation not supported).

Will change it to EOPNOTSUPP, thanks.

> 
> I am fine with both.  In any case though the aforementioned driver can
> just remove PP_FLAG_DMA_MAP and do it's own mappings.
> 
> Regards
> /Ilias
>>
>> -Jesper
>>
> .
>