netdev - 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 10:25:28 +0300
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Yunsheng Lin <linyunsheng@...wei.com>
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 Fri, 24 Sept 2021 at 10:04, Yunsheng Lin <linyunsheng@...wei.com> wrote:
>
> 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.

It rips out support for devices that are 32bit and have 64bit dma and
make the whole code easier to follow.  I thought we agreed on removing
the support for those devices regardless didn't we?

Regards
/Ilias