linux-kernel - Re: [PATCH v3] net: phy: add driver for Motorcomm yt8511 phy

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Message-ID: <CAMdYzYqQ4gaFRD8wbdm9PRpT-ZeiL6WVj_eHKnF_uF=mKx3A4g@mail.gmail.com>
Date:   Fri, 14 May 2021 10:09:18 -0400
From:   Peter Geis <pgwipeout@...il.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>
Subject: Re: [PATCH v3] net: phy: add driver for Motorcomm yt8511 phy

On Fri, May 14, 2021 at 9:09 AM Russell King (Oracle)
<linux@...linux.org.uk> wrote:
>
> Hi!
>
> On Fri, May 14, 2021 at 07:58:26AM -0400, Peter Geis wrote:
> > +     /* set rgmii delay mode */
> > +     val = __phy_read(phydev, YT8511_PAGE);
> > +
> > +     switch (phydev->interface) {
> > +     case PHY_INTERFACE_MODE_RGMII:
> > +             val &= ~(YT8511_DELAY_RX | YT8511_DELAY_TX);
> > +             break;
> > +     case PHY_INTERFACE_MODE_RGMII_ID:
> > +             val |= YT8511_DELAY_RX | YT8511_DELAY_TX;
> > +             break;
> > +     case PHY_INTERFACE_MODE_RGMII_RXID:
> > +             val &= ~(YT8511_DELAY_TX);
> > +             val |= YT8511_DELAY_RX;
> > +             break;
> > +     case PHY_INTERFACE_MODE_RGMII_TXID:
> > +             val &= ~(YT8511_DELAY_RX);
> > +             val |= YT8511_DELAY_TX;
> > +             break;
> > +     default: /* leave everything alone in other modes */
> > +             break;
> > +     }
> > +
> > +     ret = __phy_write(phydev, YT8511_PAGE, val);
> > +     if (ret < 0)
> > +             goto err_restore_page;
>
> Another way of writing the above is to set "val" to be the value of the
> YT8511_DELAY_RX and YT8511_DELAY_TX bits, and then do:
>
>         ret = __phy_modify(phydev, YT8511_PAGE,
>                            (YT8511_DELAY_RX | YT8511_DELAY_TX), val);
>         if (ret < 0)
>                 goto err_restore_page;
>
> which moves the read-modify-write out of the driver into core code and
> makes the driver code smaller. It also handles your missing error check
> on __phy_read() above - would you want the above code to attempt to
> write a -ve error number back to this register? I suspect not!

That makes sense, thanks!
I was thinking about how to use __phy_modify with a functional mask,
but it didn't click until I had already sent it in.
Also thanks for catching handling that ret on the read!

>
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!