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

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Date:   Tue, 8 Jun 2021 14:21:03 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Zhou Yanjie <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 2/2] net: stmmac: Add Ingenic SoCs MAC support.

> > > +	case PHY_INTERFACE_MODE_RGMII:
> > > +		val = FIELD_PREP(MACPHYC_TX_SEL_MASK, MACPHYC_TX_SEL_DELAY) |
> > > +			  FIELD_PREP(MACPHYC_TX_DELAY_MASK, MACPHYC_TX_DELAY_63_UNIT) |
> > > +			  FIELD_PREP(MACPHYC_RX_SEL_MASK, MACPHYC_RX_SEL_ORIGIN) |
> > > +			  FIELD_PREP(MACPHYC_PHY_INFT_MASK, MACPHYC_PHY_INFT_RGMII);
> > What exactly does MACPHYC_TX_DELAY_63_UNIT mean here? Ideally, the MAC
> > should not be adding any RGMII delays. It should however pass mode
> > through to the PHY, so it can add the delays, if the mode indicates it
> > should, e.g. PHY_INTERFACE_MODE_RGMII_ID. This is also why you should
> > be handling all 4 RGMII modes here, not just one.
> 
> 
> MACPHYC_TX_DELAY_63_UNIT means set MAC TX clk delay to 63 units (similar to the "tx-delay" in dwmac-rk.c). However, the manual does not clearly describe the time span of one unit, after consulting engineer of Ingenic, I learned that the value is recommended to be set to 63.
> I will change it to be similar to the way done in dwmac-rk.c.

Please wrap your text to around 75 characters per line.

I suspect you don't understand RGMII delays. As i said, normally, the
MAC does not add delays, the PHY does. Please take a closer look at
this.

	Andrew