netdev - Re: [PATCH] net: phy: micrel: make *-skew-ps check more lenient

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Message-ID: <bf2c71d5f73839bdc585c19490e40d08f26d644a.camel@toradex.com>
Date:   Wed, 13 Oct 2021 10:18:59 +0000
From:   Philippe Schenker <philippe.schenker@...adex.com>
To:     "matthias.schiffer@...tq-group.com" 
        <matthias.schiffer@...tq-group.com>
CC:     "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "kuba@...nel.org" <kuba@...nel.org>
Subject: Re: [PATCH] net: phy: micrel: make *-skew-ps check more lenient

On Wed, 2021-10-13 at 10:46 +0200, Matthias Schiffer wrote:
> 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.

Now I have understood your argument. But then I suggest to delete the
warning entirely as it completely changes its meaning with that patch.

Philippe

> 
> 
> > 
> > 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@...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,
> > 
> > 
>