netdev - RE: [EXT] Re: [PATCH v5 3/3] ARM: imx6plus: optionally enable internal routing of clk_enet

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Date:   Sun, 5 Jul 2020 14:45:02 +0000
From:   Andy Duan <fugang.duan@....com>
To:     Sven Van Asbroeck <thesven73@...il.com>,
        Fabio Estevam <festevam@...il.com>
CC:     Shawn Guo <shawnguo@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.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 v5 3/3] ARM: imx6plus: optionally enable
 internal routing of clk_enet_ref

From: Sven Van Asbroeck <thesven73@...il.com>
> Hi Fabio, Andy,
> 
> On Thu, Jul 2, 2020 at 6:29 PM Fabio Estevam <festevam@...il.com> wrote:
> >
> > With the device tree approach, I think that a better place to touch
> > GPR5 would be inside the fec driver.
> >
> 
> Are we 100% sure this is the best way forward, though?
> 
> All the FEC driver should care about is the FEC logic block inside the SoC. It
> should not concern itself with the way a SoC happens to bring a clock (PTP
> clock) to the input of the FEC logic block - that is purely a SoC implementation
> detail.

I also agree with that relates to SOC integration. 
> 
> It makes sense to add fsl,stop-mode (= a GPR bit) to the FEC driver, as this bit
> is a logic input to the FEC block, which the driver needs to dynamically flip.
> 
> But the PTP clock is different, because it's statically routed by the SoC.
> 
> Maybe this problem needs a clock routing solution?
> Isn't there an imx6q plus clock mux we're not modelling?
> 
>   enet_ref-o------>ext>---pad_clk--| \
>            |                       |M |----fec_ptp_clk
>            o-----------------------|_/
> 
> Where M = mux controlled by GPR5[9]
> 
> The issue here is that pad_clk is routed externally, so its parent could be any
> internal or external clock. I have no idea how to model this in the clock
> framework.
Don't consider it complex, GPR5[9] just select the rgmii gtx source from PAD or internal
Like：
GPR5[9] is cleared: PAD -> MAC gtx
GPR5[9] is set: Pll_enet -> MAC gtx
As you said, register one clock mux for the selection, assign the clock parent by board dts
file, but now current clock driver doesn't support GPR clock.