linux-kernel - Re: [PATCH v3] net: phy: Provide Module 4 KSZ9477 errata (DS80000754C)

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Message-ID: <20230831103709.GC17603@pengutronix.de>
Date:   Thu, 31 Aug 2023 12:37:09 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Lukasz Majewski <lukma@...x.de>, Tristram.Ha@...rochip.com,
        Eric Dumazet <edumazet@...gle.com>,
        Andrew Lunn <andrew@...n.ch>, davem@...emloft.net,
        Woojung Huh <woojung.huh@...rochip.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, UNGLinuxDriver@...rochip.com,
        Heiner Kallweit <hkallweit1@...il.com>,
        Michael Walle <michael@...le.cc>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Arun Ramadoss <arun.ramadoss@...rochip.com>,
        Oleksij Rempel <linux@...pel-privat.de>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] net: phy: Provide Module 4 KSZ9477 errata
 (DS80000754C)

On Thu, Aug 31, 2023 at 11:28:00AM +0100, Russell King (Oracle) wrote:
> On Thu, Aug 31, 2023 at 09:25:27AM +0200, Lukasz Majewski wrote:
> > diff --git a/include/linux/micrel_phy.h b/include/linux/micrel_phy.h
> > index 8bef1ab62bba..eed474fc7308 100644
> > --- a/include/linux/micrel_phy.h
> > +++ b/include/linux/micrel_phy.h
> > @@ -44,6 +44,7 @@
> >  #define MICREL_PHY_50MHZ_CLK	0x00000001
> >  #define MICREL_PHY_FXEN		0x00000002
> >  #define MICREL_KSZ8_P1_ERRATA	0x00000003
> > +#define MICREL_NO_EEE	0x00000004
> 
> Erm... Maybe someone should clarify this... we have in the code the
> following tests for these "flags":
> 
> 	/* Support legacy board-file configuration */
> 	if (phydev->dev_flags & MICREL_PHY_50MHZ_CLK) {
> 	        priv->rmii_ref_clk_sel = true;
> 	        priv->rmii_ref_clk_sel_val = true;
> 	}
> 
> 	/* Skip auto-negotiation in fiber mode */
> 	if (phydev->dev_flags & MICREL_PHY_FXEN) {
> 	        phydev->speed = SPEED_100;
> 	        return 0;
> 	}
> 
> 	if (phydev->dev_flags & MICREL_KSZ8_P1_ERRATA)
> 		return -EOPNOTSUPP;
> 
> 	/* According to KSZ9477 Errata DS80000754C (Module 4) all EEE modes
> 	 * in this switch shall be regarded as broken.
> 	 */
> 	if (phydev->dev_flags & MICREL_NO_EEE)
> 	        phydev->eee_broken_modes = -1;
> 
> Is it intentional that setting MICREL_PHY_50MHZ_CLK on its own also
> activates the MICREL_KSZ8_P1_ERRATA and vice versa? Is it intentional
> that setting MICREL_PHY_FXEN also activates MICREL_KSZ8_P1_ERRATA and
> vice versa?
> 
> To me, this looks horribly broken, and this patch just perpetuates the
> brokenness (but at least 0x4 doesn't overlap with the other flags.)
> 
> If it is intentional, then MICREL_KSZ8_P1_ERRATA should be defined to
> make it explicit - in other words, as
> (MICREL_PHY_FXEN|MICREL_PHY_50MHZ_CLK). If not, all these flags should
> be defined using (1 << n) or BIT() to make it explicit that they're a
> bit, and not just a hex number that gets incremented when the next flag
> is added.

Indeed, it is broken. I'll send a fix for this one.
MICREL_KSZ8_P1_ERRATA should be BIT(3)
and MICREL_NO_EEE BIT(4)

Thx!

Regards,
Oleksij
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