netdev - RE: [EXT] Re: [PATCH net-next] net: stmmac: bump tc when get underflow error from DMA descriptor

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Date:   Fri, 10 Dec 2021 03:11:16 +0000
From:   Xiaoliang Yang <xiaoliang.yang_1@....com>
To:     Jakub Kicinski <kuba@...nel.org>,
        Joakim Zhang <qiangqing.zhang@....com>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peppe.cavallaro@...com" <peppe.cavallaro@...com>,
        "alexandre.torgue@...s.st.com" <alexandre.torgue@...s.st.com>,
        "joabreu@...opsys.com" <joabreu@...opsys.com>,
        Yannick Vignon <yannick.vignon@....com>,
        "boon.leong.ong@...el.com" <boon.leong.ong@...el.com>,
        "Jose.Abreu@...opsys.com" <Jose.Abreu@...opsys.com>,
        "mst@...hat.com" <mst@...hat.com>,
        "Joao.Pinto@...opsys.com" <Joao.Pinto@...opsys.com>,
        Mingkai Hu <mingkai.hu@....com>, Leo Li <leoyang.li@....com>
Subject: RE: [EXT] Re: [PATCH net-next] net: stmmac: bump tc when get
 underflow error from DMA descriptor

Hi Jakub,

On Fri, 10 Dec 2021 10:41:00 +0800 Jakub Kicinski wrote:
> > > net: stmmac: bump tc when get underflow error from DMA descriptor
> > >
> > > In DMA threshold mode, frame underflow errors may sometimes occur
> > > when the TC(threshold control) value is not enough. The TC value
> > > need to be bumped up in this case.
> > >
> > > There is no underflow interrupt bit on DMA_CH(#i)_Status of dwmac4,
> > > so the DMA threshold cannot be bumped up in stmmac_dma_interrupt().
> > > The i.mx8mp board observed an underflow error while running NFS
> > > boot, the NFS rootfs could not be mounted.
> > >
> > > The underflow error can be got from the DMA descriptor TDES3 on
> dwmac4.
> > > This patch bump up tc value once underflow error is got from TDES3.
> > >
> > > Signed-off-by: Xiaoliang Yang <xiaoliang.yang_1@....com>
> >
> > 5 queues with FIFO cut-through mode can work well after applying this
> patch.
> 
> This never worked, correct? It's not a regression fix?
Yes, it's never worked when the underflow error is observed in the case of NFS boot on i.mx8mp. I'm not sure if other SoC have same issue in this case, but I think it's necessary to increase the threshold value in case of underflow error.
Do you mean that I need to send the patch as a bug fix to net branch?

Regards,
Xiaoliang