linux-kernel - Re: [PATCH v2 2/2] net: stmmac: Add Ingenic SoCs MAC support.

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Message-ID: <YMYy6JMSHm1Cqdt2@lunn.ch>
Date:   Sun, 13 Jun 2021 18:31:36 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     周琰杰 <zhouyanjie@...yeetech.com>
Cc:     davem@...emloft.net, kuba@...nel.org, robh+dt@...nel.org,
        peppe.cavallaro@...com, alexandre.torgue@...s.st.com,
        joabreu@...opsys.com, mcoquelin.stm32@...il.com,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, dongsheng.qiu@...enic.com,
        aric.pzqi@...enic.com, rick.tyliu@...enic.com,
        sihui.liu@...enic.com, jun.jiang@...enic.com,
        sernia.zhou@...mail.com, paul@...pouillou.net
Subject: Re: [PATCH v2 2/2] net: stmmac: Add Ingenic SoCs MAC support.

On Sun, Jun 13, 2021 at 04:34:52PM +0800, 周琰杰 wrote:
> 于 Thu, 10 Jun 2021 16:57:29 +0200
> Andrew Lunn <andrew@...n.ch> 写道:
> 
> > > Here is Ingenic's reply, the time length corresponding to a unit is
> > > 19.5ps (19500fs).  
> > 
> > Sometimes, there is a negative offset in the delays. So a delay value
> > of 0 written to the register actually means -200ps or something.
> 
> Ah, perhaps this explains why we still need to add fine-tuning
> parameter in rgmii-id and rgmii-txid modes to ensure that the network
> works properly.

Please try to find this out. rgmii means no delay. If the hardware is
doing -500pS by default, you need to take this into account, and add
the 500pS back on.

    Andrew