Date:   Tue, 31 Mar 2020 19:16:59 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     David Jander <david@...tonic.nl>, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        netdev@...r.kernel.org, Sascha Hauer <s.hauer@...gutronix.de>,
        linux-kernel@...r.kernel.org, linux-imx@....com,
        kernel@...gutronix.de, Shawn Guo <shawnguo@...nel.org>,
        Fabio Estevam <festevam@...il.com>,
        linux-arm-kernel@...ts.infradead.org,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [PATCH v2] ARM: imx: allow to disable board specific PHY fixups

On Tue, Mar 31, 2020 at 06:03:00PM +0100, Russell King - ARM Linux admin wrote:
> On Tue, Mar 31, 2020 at 10:44:59AM +0200, David Jander wrote:
> > I have checked with the datasheet of the AR8035, and AFAICS, what the code
> > does is this:
> > 
> >  - Disable the SmartEEE feature of the phy. The comment in the code implies
> >    that for some reason it doesn't work, but the reason itself is not given.
> >    Anyway, disabling SmartEEE should IMHO opinion be controlled by a DT
> >    setting. There is no reason to believe this problem is specific to the
> >    i.MX6. Besides, it is a feature of the phy, so it seems logical to expose
> >    that via the DT. Once that is done, it has no place here.
> > 
> >  - Set the external clock output to 125MHz. This is needed because the i.MX6
> >    needs a 125MHz reference clock input. But it is not a requirement to use
> >    this output. It is perfectly fine and possible to design a board that uses
> >    an external oscillator for this. It is also possible that an i.MX6 design
> >    has such a phy connected to a MAC behind a switch or some other interface.
> >    Independent of i.MX6 this setting can also be necessary for other hardware
> >    designs, based on different SoC's. In summary, this is a feature of the
> >    specific hardware design at hand, and has nothing to do with the i.MX6
> >    specifically. This should definitely be exposed through the DT and not be
> >    here.
> > 
> >  - Enable TXC delay. To clarify, the RGMII specification version 1 specified
> >    that the RXC and TXC traces should be routed long enough to introduce a
> >    certain delay to the clock signal, or the delay should be introduced via
> >    other means. In a later version of the spec, a provision was given for MAC
> >    or PHY devices to generate this delay internally. The i.MX6 MAC interface
> >    is unable to generate the required delay internally, so it has to be taken
> >    care of either by the board layout, or by the PHY device. This is the
> >    crucial point: The amount of delay set by the PHY delay register depends on
> >    the board layout. It should NEVER be hard-coded in SoC setup code. The
> >    correct way is to specify it in the DT. Needless to say that this too,
> >    isn't i.MX6-specific.
> 
> Let's say this is simple to do, shall we?
> 
> So, if I disable the call to ar8031_phy_fixup() from ar8035_phy_fixup(),
> and add the following to the imx6qdl-sr-som.dtsi fragment:
> 
> &fec {
> ...
>         phy-handle = <&phy>;
> 
>         mdio {
>                 #address-cells = <1>;
>                 #size-cells = <0>;
> 
>                 phy: ethernet-phy@0 {
>                         reg = <0>;
>                         qca,clk-out-frequency = <125000000>;
>                 };
>         };
> };
> 
> Note that phy-mode is already RGMII-ID.  This should work, right?
> 
> The link still comes up, which is good, but the PHY registers for
> the clock output are wrong.
> 
> MMD 3 register 0x8016 contains 0xb282, not 0xb29a which it has
> _with_ the quirk - and thus the above clock frequency stated in
> DT is not being selected.  Forcing this register to the right
> value restores networking.
> 
> Yes, the PHY driver is being used:
> 
> Qualcomm Atheros AR8035 2188000.ethernet-1:00: attached PHY driver [Qualcomm Atheros AR8035] (mii_bus:phy_addr=2188000.ethernet-1:00, irq=POLL)
> 
> So that's not the problem.
> 
> Adding some debug shows that the phy_device that is being used is
> the correct one:
> 
> Qualcomm Atheros AR8035 2188000.ethernet-1:00: node=/soc/aips-bus@...0000/ethernet@...8000/mdio/ethernet-phy@0
> 
> and it is correctly parsing the clk-out-frequency property:
> 
> Qualcomm Atheros AR8035 2188000.ethernet-1:00: cof=0 125000000
> 
> When we get to attaching the PHY however:
> 
> Qualcomm Atheros AR8035 2188000.ethernet-1:00: clk_25m_mask=0004 clk_25m_reg=0000
> 
> which is just wrong.  That's because:
> 
>                 if (at803x_match_phy_id(phydev, ATH8030_PHY_ID) ||
>                     at803x_match_phy_id(phydev, ATH8035_PHY_ID)) {
>                         priv->clk_25m_reg &= ~AT8035_CLK_OUT_MASK;
>                         priv->clk_25m_mask &= ~AT8035_CLK_OUT_MASK;
>                 }
> 
> is patently untested - those "~" should not be there.  These masks
> are one-bits-set for the values that comprise the fields, not
> zero-bits-set.
> 
> So, I see a patch series is going to be necessary to fix the cockup(s)
> in the PHY driver before we can do anything with DT files.

I'm glad you found this issues :D I made a patch to fix it last week.
And it was a reason to send a patch for disabling _all_ fixups :)

Regards,
Oleksij

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