netdev - Re: [EXT] Re: Fwd: net: fec: rx descriptor ring out of order

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Message-ID: <CAMeyCbiuFAtqpUTtrPx3Afp_Hc41nZTzq0US7vg5HXwPp6SdFQ@mail.gmail.com>
Date:   Sat, 14 Nov 2020 18:36:51 +0100
From:   Kegl Rohit <keglrohit@...il.com>
To:     Andy Duan <fugang.duan@....com>
Cc:     David Laight <David.Laight@...lab.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [EXT] Re: Fwd: net: fec: rx descriptor ring out of order

On Sat, Nov 14, 2020 at 2:58 AM Andy Duan <fugang.duan@....com> wrote:
>
> From: Kegl Rohit <keglrohit@...il.com> Sent: Friday, November 13, 2020 8:21 PM
> > On Fri, Nov 13, 2020 at 8:33 AM Kegl Rohit <keglrohit@...il.com> wrote:
> > >
> > > > What are the addresses of the ring entries?
> > > > I bet there is something wrong with the cache coherency and/or
> > > > flushing.
> > > >
> > > > So the MAC hardware has done the write but (somewhere) it isn't
> > > > visible to the cpu for ages.
> > >
> > > CMA memory is disabled in our kernel config.
> > > So the descriptors allocated with dma_alloc_coherent() won't be CMA memory.
> > > Could this cause a different caching/flushing behaviour?
> >
> > Yes, after tests I think it is caused by the disabled CMA.
> >
> > @Andy
> > I could find this mail and the attached "i.MX6 dma memory bufferable
> > issue.pptx" in the archive
> > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmarc.info
> > %2F%3Fl%3Dlinux-netdev%26m%3D140135147823760&amp;data=04%7C01
> > %7Cfugang.duan%40nxp.com%7C121e73ec66684a125e2a08d887cea578%7C
> > 686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637408668924362983
> > %7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJ
> > BTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=e7Cm24Ay1Ay52UKtzT
> > BiX9KlhuublndP30vnwxAaugM%3D&amp;reserved=0
> > Was this issue solved in some kernel versions later on?
> > Is CMA still necessary with a 5.4 Kernel?
>
> Yes, CMA is required. Otherwise it requires one patch for L2 cache.

Where can I find the patch / is the patch already mainline?
Is it some development patch or already well tested?
Or would you recommend enabling CMA instead?
Are other components affected apart from the already mentioned
peripherals (ENET, Audio, USB) in the attachment?