netdev - Re: [PATCH] net: fec: Fix PHY init after phy_reset_after_clk

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Message-ID: <20200903220847.GI3112546@lunn.ch>
Date:   Fri, 4 Sep 2020 00:08:47 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Marek Vasut <marex@...x.de>
Cc:     netdev@...r.kernel.org,
        Christoph Niedermaier <cniedermaier@...electronics.com>,
        "David S . Miller" <davem@...emloft.net>,
        NXP Linux Team <linux-imx@....com>,
        Richard Leitner <richard.leitner@...data.com>,
        Shawn Guo <shawnguo@...nel.org>
Subject: Re: [PATCH] net: fec: Fix PHY init after phy_reset_after_clk_enable()

> > b4 am 20200903043947.3272453-1-f.fainelli@...il.com
> 
> That might be a fix for the long run, but I doubt there's any chance to
> backport it all to stable, is there ?

No. For stable we need something simpler.

> >>> I think a better fix for the original problem is for the SMSC PHY
> >>> driver to control the clock itself. If it clk_prepare_enables() the
> >>> clock, it knows it will not be shut off again by the FEC run time
> >>> power management.
> >>
> >> The FEC MAC is responsible for generating the clock, the PHY clock are
> >> not part of the clock framework as far as I can tell.
> > 
> > I'm not sure this is true. At least:
> > 
> > https://elixir.bootlin.com/linux/latest/source/arch/arm/boot/dts/imx6ul-kontron-n6x1x-s.dtsi#L123
> > 
> > and there are a few more examples:
> > 
> > imx6ul-14x14-evk.dtsi:			clocks = <&clks IMX6UL_CLK_ENET_REF>;
> > imx6ul-kontron-n6x1x-s.dtsi:			clocks = <&clks IMX6UL_CLK_ENET_REF>;
> > imx6ul-kontron-n6x1x-som-common.dtsi:			clocks = <&clks IMX6UL_CLK_ENET_REF>;
> > imx6ull-myir-mys-6ulx.dtsi:			clocks = <&clks IMX6UL_CLK_ENET_REF>;
> > imx6ul-phytec-phycore-som.dtsi:			clocks = <&clks IMX6UL_CLK_ENET_REF>;
> > 
> > Maybe it is just IMX6?
> 
> This is reference clock for the FEC inside the SoC, you probably want to
> control the clock going out of the SoC and into the PHY, which is
> different clock than the one described in the DT, right ?

I _think_ this is the external clock which is feed to the PHY. Why
else put it in the phy node in DT? And it has the name "rmii-ref"
which again suggests it is the RMII clock, not something internal to
the FEC.

To be sure, we would need to check the datasheet.

   Andrew