The StarFive VisionFive V1 SBC uses a Motorcomm YT8521 PHY supporting
RGMII-ID, but requires manual adjustment of the RX internal delay to
work properly.

The default RX delay provided by the driver is 1.95 ns, which proves to
be too high. Applying a 50% reduction seems to mitigate the issue.

Also note this adjustment is not necessary on BeagleV Starlight SBC,
which uses a Microchip PHY.  Hence, there is no indication of a
miss-behaviour on the GMAC side, but most likely the issue stems from
the Motorcomm PHY.

Co-developed-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
---
 .../boot/dts/starfive/jh7100-starfive-visionfive-v1.dts    | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/riscv/boot/dts/starfive/jh7100-starfive-visionfive-v1.dts b/arch/riscv/boot/dts/starfive/jh7100-starfive-visionfive-v1.dts
index e82af72f1aaf..ca134b9f11bf 100644
--- a/arch/riscv/boot/dts/starfive/jh7100-starfive-visionfive-v1.dts
+++ b/arch/riscv/boot/dts/starfive/jh7100-starfive-visionfive-v1.dts
@@ -18,3 +18,10 @@ gpio-restart {
 		priority = <224>;
 	};
 };
+
+&mdio {
+	phy: ethernet-phy@0 {
+		reg = <0>;
+		rx-internal-delay-ps = <900>;
+	};
+};
-- 
2.43.0

On Fri, Dec 15, 2023 at 10:40:45PM +0200, Cristian Ciocaltea wrote:
> The StarFive VisionFive V1 SBC uses a Motorcomm YT8521 PHY supporting
> RGMII-ID, but requires manual adjustment of the RX internal delay to
> work properly.
> 
> The default RX delay provided by the driver is 1.95 ns, which proves to
> be too high. Applying a 50% reduction seems to mitigate the issue.
> 
> Also note this adjustment is not necessary on BeagleV Starlight SBC,
> which uses a Microchip PHY.  Hence, there is no indication of a
> miss-behaviour on the GMAC side, but most likely the issue stems from
> the Motorcomm PHY.

I suggest you make a similar comment in the .dts file, just to explain
the odd setting.

	Andrew

On 12/17/23 19:55, Andrew Lunn wrote:
> On Fri, Dec 15, 2023 at 10:40:45PM +0200, Cristian Ciocaltea wrote:
>> The StarFive VisionFive V1 SBC uses a Motorcomm YT8521 PHY supporting
>> RGMII-ID, but requires manual adjustment of the RX internal delay to
>> work properly.
>>
>> The default RX delay provided by the driver is 1.95 ns, which proves to
>> be too high. Applying a 50% reduction seems to mitigate the issue.
>>
>> Also note this adjustment is not necessary on BeagleV Starlight SBC,
>> which uses a Microchip PHY.  Hence, there is no indication of a
>> miss-behaviour on the GMAC side, but most likely the issue stems from
>> the Motorcomm PHY.
> 
> I suggest you make a similar comment in the .dts file, just to explain
> the odd setting.

Sure, will do, we need a v4 anyway.

Thanks,
Cristian