RE: [PATCH net v2] net: phy: marvell: add Marvell specific PHY loopback

[Ismail, Mohammad Athari]

> -----Original Message-----
> From: Russell King <linux@xxxxxxxxxxxxxxx>
> Sent: Wednesday, January 12, 2022 9:13 PM
> To: Ismail, Mohammad Athari <mohammad.athari.ismail@xxxxxxxxx>
> Cc: Andrew Lunn <andrew@xxxxxxx>; David S . Miller
> <davem@xxxxxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>; Oleksij
> Rempel <linux@xxxxxxxxxxxxxxxx>; Heiner Kallweit
> <hkallweit1@xxxxxxxxx>; netdev@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; stable@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH net v2] net: phy: marvell: add Marvell specific PHY
> loopback
> 
> On Wed, Jan 12, 2022 at 05:33:44PM +0800, Mohammad Athari Bin Ismail
> wrote:
> > +static int marvell_loopback(struct phy_device *phydev, bool enable) {
> > +	if (enable) {
> > +		u16 bmcr_ctl = 0, mscr2_ctl = 0;
> > +
> > +		if (phydev->speed == SPEED_1000)
> > +			bmcr_ctl = BMCR_SPEED1000;
> > +		else if (phydev->speed == SPEED_100)
> > +			bmcr_ctl = BMCR_SPEED100;
> > +
> > +		if (phydev->duplex == DUPLEX_FULL)
> > +			bmcr_ctl |= BMCR_FULLDPLX;
> > +
> > +		phy_modify(phydev, MII_BMCR, ~0, bmcr_ctl);
> 
> Is there any point in doing a read-modify-write here if you're just setting all
> bits in the register? Wouldn't phy_write() be more appropriate? What about
> error handing?

Yes, you're right. phy_write() is more suitable. And will add error handling as well.
Will include them in v3 patch.

> 
> > +
> > +		if (phydev->speed == SPEED_1000)
> > +			mscr2_ctl = BMCR_SPEED1000;
> > +		else if (phydev->speed == SPEED_100)
> > +			mscr2_ctl = BMCR_SPEED100;
> > +
> > +		phy_modify_paged(phydev, MII_MARVELL_MSCR_PAGE,
> > +				 MII_88E1510_MSCR_2, BMCR_SPEED1000 |
> > +				 BMCR_SPEED100, mscr2_ctl);
> > +

I believe this also need error handling.

> > +		/* Need soft reset to have speed configuration takes effect
> */
> > +		genphy_soft_reset(phydev);

Ditto.

> > +
> > +		/* FIXME: Based on trial and error test, it seem 1G need to
> have
> > +		 * delay between soft reset and loopback enablement.
> > +		 */
> > +		if (phydev->speed == SPEED_1000)
> > +			msleep(1000);
> > +
> > +		return phy_modify(phydev, MII_BMCR, BMCR_LOOPBACK,
> > +				  BMCR_LOOPBACK);
> > +	} else {
> > +		phy_modify(phydev, MII_BMCR, BMCR_LOOPBACK, 0);
> 
> Error handling?

Will add it in v3 patch.

-Athari-


> 
> Thanks.
> 
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