netdev - Re: [RFC PATCH net-next v3 19/20] net: dsa: qca8k: pass switch_revision info to phy dev

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Date:   Sat, 8 May 2021 00:33:53 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Ansuel Smith <ansuelsmth@...il.com>
Cc:     Vladimir Oltean <olteanv@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH net-next v3 19/20] net: dsa: qca8k: pass
 switch_revision info to phy dev_flags

On Sat, May 08, 2021 at 01:26:02AM +0200, Ansuel Smith wrote:
> On Thu, May 06, 2021 at 02:24:58PM +0300, Vladimir Oltean wrote:
> > On Wed, May 05, 2021 at 12:29:13AM +0200, Ansuel Smith wrote:
> > > Define get_phy_flags to pass switch_Revision needed to tweak the
> > > internal PHY with debug values based on the revision.
> > > 
> > > Signed-off-by: Ansuel Smith <ansuelsmth@...il.com>
> > > ---
> > >  drivers/net/dsa/qca8k.c | 19 +++++++++++++++++++
> > >  1 file changed, 19 insertions(+)
> > > 
> > > diff --git a/drivers/net/dsa/qca8k.c b/drivers/net/dsa/qca8k.c
> > > index b4cd891ad35d..237e09bb1425 100644
> > > --- a/drivers/net/dsa/qca8k.c
> > > +++ b/drivers/net/dsa/qca8k.c
> > > @@ -1654,6 +1654,24 @@ qca8k_port_vlan_del(struct dsa_switch *ds, int port,
> > >  	return ret;
> > >  }
> > >  
> > > +static u32 qca8k_get_phy_flags(struct dsa_switch *ds, int port)
> > > +{
> > > +	struct qca8k_priv *priv = ds->priv;
> > > +
> > > +	pr_info("revision from phy %d", priv->switch_revision);
> > 
> > Log spam.
> > 
> > > +	/* Communicate to the phy internal driver the switch revision.
> > > +	 * Based on the switch revision different values needs to be
> > > +	 * set to the dbg and mmd reg on the phy.
> > > +	 * The first 2 bit are used to communicate the switch revision
> > > +	 * to the phy driver.
> > > +	 */
> > > +	if (port > 0 && port < 6)
> > > +		return priv->switch_revision;
> > > +
> > > +	return 0;
> > > +}
> > > +
> > >  static enum dsa_tag_protocol
> > >  qca8k_get_tag_protocol(struct dsa_switch *ds, int port,
> > >  		       enum dsa_tag_protocol mp)
> > > @@ -1687,6 +1705,7 @@ static const struct dsa_switch_ops qca8k_switch_ops = {
> > >  	.phylink_mac_config	= qca8k_phylink_mac_config,
> > >  	.phylink_mac_link_down	= qca8k_phylink_mac_link_down,
> > >  	.phylink_mac_link_up	= qca8k_phylink_mac_link_up,
> > > +	.get_phy_flags		= qca8k_get_phy_flags,
> > >  };
> > >  
> > >  static int qca8k_read_switch_id(struct qca8k_priv *priv)
> > > -- 
> > > 2.30.2
> > > 
> > 
> > Florian, I think at one point you said that a correct user of
> > phydev->dev_flags should first check the PHY revision and not apply
> > dev_flags in blind, since they are namespaced to each PHY driver?
> > It sounds a bit circular to pass the PHY revision to the PHY through
> > phydev->dev_flags, either that or I'm missing some piece.
> 
> Just to make sure. This is the SWITCH revision not the PHY revision. It
> was pointed out in old version that I should get this value from the PHY
> regs but they are different values. This is why the dsa driver needs to
> use the dev_flags to pass the SWITCH revision to the phy driver. Am I
> implementing this in the wrong way and I should declare something to
> pass this value in a more standard way? (anyway i'm pushing v4 so i
> don't know if we should continue that there)

Vladimir is confused - it is not PHY revision at all, but the PHY
identifiers.

What was actually suggested was checking the PHY identifiers before
passing PHY-driver specific flags, so that we didn't end up setting
driver private flags that are intending for one driver, but end up
actually binding a different driver, and mis-interpreting the flags.

This is one of the problems of the current scheme: it's just a
meaningless opaque u32 variable with no defined structure to it that
the various PHY drivers themselves use in whatever way they see fit.
That is only fine to use _if_ you know for certain which driver is
going to bind ahead of time.

As I mentioned in direct reply to your patch, there was discussions
about this back in February, but they seem to have stalled.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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