On Wed, Nov 30, 2016 at 10:44 PM, Rob Herring [off-list ref] wrote:

On Fri, Nov 25, 2016 at 02:01:50PM +0100, Martin Blumenstingl wrote:

quoted

This allows configuring the RGMII TX clock delay. The RGMII clock is
generated by underlying hardware of the the Meson 8b / GXBB DWMAC glue.
The configuration depends on the actual hardware (no delay may be
needed due to the design of the actual circuit, the PHY might add this
delay, etc.).

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
---
 Documentation/devicetree/bindings/net/meson-dwmac.txt | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/Documentation/devicetree/bindings/net/meson-dwmac.txt b/Documentation/devicetree/bindings/net/meson-dwmac.txt
index 89e62dd..f8bc540 100644
--- a/Documentation/devicetree/bindings/net/meson-dwmac.txt
+++ b/Documentation/devicetree/bindings/net/meson-dwmac.txt

@@ -25,6 +25,20 @@ Required properties on Meson8b and newer:
              - "clkin0" - first parent clock of the internal mux
              - "clkin1" - second parent clock of the internal mux

+Optional properties on Meson8b and newer:
+- amlogic,tx-delay-ns:       The internal RGMII TX clock delay (provided
+                     by this driver) in nanoseconds. Allowed values
+                     are: 0ns, 2ns, 4ns, 6ns.
+                     This must be configured when the phy-mode is
+                     "rgmii" (typically a value of 2ns is used in
+                     this case).
+                     When phy-mode is set to "rgmii-id" or
+                     "rgmii-txid" the TX clock delay is already
+                     provided by the PHY. In that case this
+                     property should be set to 0ns (which disables
+                     the TX clock delay in the MAC to prevent the
+                     clock from going off because both PHY and MAC
+                     are adding a delay).

What's the default? Why can't no property mean 0ns delay?

This value (2ns) was previously hardcoded. Having a default of 0ns
means that patch 7 ("ARM64: dts: amlogic: add the ethernet TX delay
configuration") becomes mandatory (otherwise we'll have broken Gbit
ethernet again because the TX delay is now disabled in the PHY when
phy-mode is "rgmii" and additionally we don't apply the 2ns TX delay
on the MAC side when the property is missing).
I'm fine with either way though - just let me know so I can adjust the
code accordingly.