linux-kernel - Re: [EXT] Re: [PATCH v4 2/2] ARM: imx6plus: enable internal routing of clk_enet

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Message-ID: <CAGngYiV9HqxSLV=PCPg10vqVC-SaayF5wakcWs2gBbXxgcUEPQ@mail.gmail.com>
Date:   Tue, 30 Jun 2020 11:23:45 -0400
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     Andy Duan <fugang.duan@....com>
Cc:     Fabio Estevam <festevam@...il.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        dl-linux-imx <linux-imx@....com>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [EXT] Re: [PATCH v4 2/2] ARM: imx6plus: enable internal routing
 of clk_enet_ref where possible

Andy, Fabio,

On Tue, Jun 30, 2020 at 2:36 AM Andy Duan <fugang.duan@....com> wrote:
>
> Sven, no matter PHY supply 125Mhz clock to pad or not,  GPR5[9] is to select RGMII
> gtx clock source from:
> - 0 Clock from pad
> - 1 Clock from PLL
>
> Since i.MX6QP can internally supply clock to MAC, we can set GPR5[9] bit by default.

That's true. But on the sabresd I notice that the PHY's ref_clk output
is from CLK_25M.
The default ref_clk freq for that PHY is 25 MHz, and I don't see anyone change
the default in the devicetree. I also see that a 25 MHz crystal is fitted, which
also suggests 25 Mhz output.

On the imx6, the default ref_clk frequency from ANATOP is 50Mhz. I don't
see anyone change that default in the devicetree either.

So is it possible that, when we switch GPR5[9] on, the external 25MHz clock
is replaced by the internal 50MHz clock? If so, I'm not sure it'll work...?