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 [off-list ref] wrote:

On 9/17/20 8:57 AM, Geert Uytterhoeven wrote:

quoted

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@glider.be>
Reviewed-by: Sergei Shtylyov <redacted>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>

quoted

@@ -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@linux-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