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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Message-ID: <CAC_iWjJLCQNHxgbQ-mzLC3OC-m2s7qj3YAtw7vPAKGG6WxywpA@mail.gmail.com>
Date:   Thu, 23 Sep 2021 13:02:05 +0300
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc:     Yunsheng Lin <linyunsheng@...wei.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

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).

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
>