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Message-ID: <987224f4ca93f928c8ddb69710d3aa72b336b6dc.camel@ew.tq-group.com>
Subject: Re: [PATCH] net: phy: micrel: make *-skew-ps check more lenient
From:   Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
To:     Philippe Schenker <philippe.schenker@toradex.com>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "kuba@kernel.org" <kuba@kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux@armlinux.org.uk" <linux@armlinux.org.uk>,
        "hkallweit1@gmail.com" <hkallweit1@gmail.com>,
        "andrew@lunn.ch" <andrew@lunn.ch>
Date:   Wed, 13 Oct 2021 10:46:19 +0200
In-Reply-To: <45137d2d365d5737f36fa398ee815695722b04e5.camel@toradex.com>
References: <20211012103402.21438-1-matthias.schiffer@ew.tq-group.com>
         <45137d2d365d5737f36fa398ee815695722b04e5.camel@toradex.com>
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On Wed, 2021-10-13 at 08:25 +0000, Philippe Schenker wrote:
> On Tue, 2021-10-12 at 12:34 +0200, Matthias Schiffer wrote:
> > It seems reasonable to fine-tune only some of the skew values when
> > using
> > one of the rgmii-*id PHY modes, and even when all skew values are
> > specified, using the correct ID PHY mode makes sense for documentation
> > purposes. Such a configuration also appears in the binding docs in
> > Documentation/devicetree/bindings/net/micrel-ksz90x1.txt, so the
> > driver
> > should not warn about it.
> 
> I don't think your commit message is right. The rgmii-*id PHY modes are
> no longer just for documentation purposes on KSZ9031 PHY. They are used
> to set the skew-registers according to .

Yes, this was implemented in [1]. The commit message explicitly states
that fine-tuning is still possible using *-skew-ps.

> 
> The warning is there, that in case you override the skew registers of
> one of the modes rgmii-id, rgmii-txid, rgmii-rxid with *-skew-ps
> settings in DT.

The "rgmii" mode should not be handled differently from "rgmii-*id" in
my opinion. Otherwise for a device that is basically "rgmii-id", but
requires slight fine-tuning, you have to set the mode to the incorrect
value "rgmii" in the DTS to avoid this warning.


> 
> Therefore I also think the warning is valuable and should be kept. We
> may want to reword it though.
> 
> Philippe

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/net/phy/micrel.c?id=bcf3440c6dd78bfe5836ec0990fe36d7b4bb7d20


> 
> > 
> > Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
> > ---
> >  drivers/net/phy/micrel.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/phy/micrel.c b/drivers/net/phy/micrel.c
> > index c330a5a9f665..03e58ebf68af 100644
> > --- a/drivers/net/phy/micrel.c
> > +++ b/drivers/net/phy/micrel.c
> > @@ -863,9 +863,9 @@ static int ksz9031_config_init(struct phy_device
> > *phydev)
> >                                 MII_KSZ9031RN_TX_DATA_PAD_SKEW, 4,
> >                                 tx_data_skews, 4, &update);
> >  
> > -               if (update && phydev->interface !=
> > PHY_INTERFACE_MODE_RGMII)
> > +               if (update && !phy_interface_is_rgmii(phydev))
> >                         phydev_warn(phydev,
> > -                                   "*-skew-ps values should be used
> > only with phy-mode = \"rgmii\"\n");
> > +                                   "*-skew-ps values should be used
> > only with RGMII PHY modes\n");
> >  
> >                 /* Silicon Errata Sheet (DS80000691D or DS80000692D):
> >                  * When the device links in the 1000BASE-T slave mode
> > only,
> 
>