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:   Fri, 24 Sep 2021 15:04:07 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Ilias Apalodimas <ilias.apalodimas@...aro.org>
CC:     Jesper Dangaard Brouer <jbrouer@...hat.com>,
        "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 21:07, Ilias Apalodimas wrote:
> On Thu, Sep 23, 2021 at 07:13:11PM +0800, Yunsheng Lin wrote:
>> 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.
> 
> Mind sending this one separately (and you can keep my reviewed-by).  It
> fits nicely on it's own and since I am not sure about the rest of the
> changes yet, it would be nice to get this one in.

I am not sure sending this one separately really makes sense, as it is
mainly used to make supporting the "keep track of pp page when __skb_frag_ref()
is called" in patch 5 easier.

> 
> Cheers
> /Ilias
>>
>>>
>>> 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
>>>>
>>> .
>>>
> .
>