netdev - Re: [PATCH net-next v4 5/5] ravb: Add support for explicit internal clock delay configuration

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Date:   Fri, 18 Sep 2020 11:04:02 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Dan Murphy <dmurphy@...com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Sergei Shtylyov <sergei.shtylyov@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Oleksij Rempel <linux@...pel-privat.de>,
        Philippe Schenker <philippe.schenker@...adex.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Kazuya Mizuguchi <kazuya.mizuguchi.ks@...esas.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Magnus Damm <magnus.damm@...il.com>,
        netdev <netdev@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v4 5/5] ravb: Add support for explicit internal
 clock delay configuration

Hi Dan,

On Thu, Sep 17, 2020 at 8:50 PM Dan Murphy <dmurphy@...com> wrote:
> On 9/17/20 8:57 AM, Geert Uytterhoeven wrote:
> > Some EtherAVB variants support internal clock delay configuration, which
> > can add larger delays than the delays that are typically supported by
> > the PHY (using an "rgmii-*id" PHY mode, and/or "[rt]xc-skew-ps"
> > properties).
> >
> > Historically, the EtherAVB driver configured these delays based on the
> > "rgmii-*id" PHY mode.  This caused issues with PHY drivers that
> > implement PHY internal delays properly[1].  Hence a backwards-compatible
> > workaround was added by masking the PHY mode[2].
> >
> > Add proper support for explicit configuration of the MAC internal clock
> > delays using the new "[rt]x-internal-delay-ps" properties.
> > Fall back to the old handling if none of these properties is present.
> >
> > [1] Commit bcf3440c6dd78bfe ("net: phy: micrel: add phy-mode support for
> >      the KSZ9031 PHY")
> > [2] Commit 9b23203c32ee02cd ("ravb: Mask PHY mode to avoid inserting
> >      delays twice").
> >
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> > Reviewed-by: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
> > Reviewed-by: Florian Fainelli <f.fainelli@...il.com>

> > @@ -1989,20 +1986,41 @@ static const struct soc_device_attribute ravb_delay_mode_quirk_match[] = {
> >   };
> >
> >   /* Set tx and rx clock internal delay modes */
> > -static void ravb_parse_delay_mode(struct net_device *ndev)
> > +static void ravb_parse_delay_mode(struct device_node *np, struct net_device *ndev)
> >   {
> >       struct ravb_private *priv = netdev_priv(ndev);
> > +     bool explicit_delay = false;
> > +     u32 delay;
> > +
> > +     if (!of_property_read_u32(np, "rx-internal-delay-ps", &delay)) {
> > +             /* Valid values are 0 and 1800, according to DT bindings */
> > +             priv->rxcidm = !!delay;
> > +             explicit_delay = true;
> > +     }
> > +     if (!of_property_read_u32(np, "tx-internal-delay-ps", &delay)) {
> > +             /* Valid values are 0 and 2000, according to DT bindings */
> > +             priv->txcidm = !!delay;
> > +             explicit_delay = true;
> > +     }
> There are helper functions for this
>
> s32 phy_get_internal_delay(struct phy_device *phydev, struct device
> *dev, const int *delay_values, int size, bool is_rx)

That helper operates on the PHY device, not on the MAC device.
Cfr. what I stated in the cover letter:

    This can be considered the MAC counterpart of commit 9150069bf5fc0e86
    ("dt-bindings: net: Add tx and rx internal delays"), which applies to
    the PHY.  Note that unlike commit 92252eec913b2dd5 ("net: phy: Add a
    helper to return the index for of the internal delay"), no helpers are
    provided to parse the DT properties, as so far there is a single user
    only, which supports only zero or a single fixed value.  Of course such
    helpers can be added later, when the need arises, or when deemed useful
    otherwise.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds