netdev - Re: [PATCH] net: fs_enet: sync rx dma buffer before reading

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Date:   Mon, 23 May 2022 13:23:36 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Måns Rullgård <mans@...sr.com>,
        Pantelis Antoniou <pantelis.antoniou@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Vitaly Bordug <vbordug@...mvista.com>,
        Dan Malek <dan@...eddededge.com>,
        Joakim Tjernlund <joakim.tjernlund@...entis.se>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: fs_enet: sync rx dma buffer before reading

On Sat, 21 May 2022 10:44:30 -0700 Jakub Kicinski wrote:
> > Well, I say the contrary.
> > 
> > On the mainline the patch may be applied as is, it won't harm.
> > 
> > However, it is gets applied to kernel 4.9 (based on the fixes: tag), it 
> > will break the driver for at least powerpc 8xx.  
> 
> I see, we should make a note of that in the commit message so it doesn't
> get sucked into stable.
> 
> > I don't know how SWIOTLB works or even what it is, does any of the 
> > microcontrollers embedding freescale ethernet uses that at all ?  
> 
> AFAIU SWIOTLB basically forces the use of bounce buffers even if the
> device can reach the entire DRAM. I think some people also use it for
> added security? IDK. I mostly use it to check if I'm using the DMA API
> "right" :)

If what I said makes sense please repost the patch, the current version
has been dropped from patchwork already.