[net-next PATCH v2 0/3] net: mdio-ipq4019: fix wrong default MDC rate

Christian Marangi
2024-01-30T00:36:02Z

This was a long journey to arrive and discover this problem.

To not waste too much char, there is a race problem with PHY and driver
probe. This was observed with Aquantia PHY firmware loading.

With some hacks the race problem was workarounded but an interesting
thing was notice. It took more than a minute for the firmware to load
via MDIO.

This was strange as the same operation was done by UBoot in at max 5
second and the same data was loaded.

A similar problem was observed on a mtk board that also had an
Aquantia PHY where the load was very slow. It was notice that the cause
was the MDIO bus running at a very low speed and the firmware
was missing a property (present in mtk sdk) that set the right frequency
to the MDIO bus.

It was fun to find that THE VERY SAME PROBLEM is present on IPQ in a
different form. The MDIO apply internally a division to the feed clock
resulting in the bus running at 390KHz instead of 6.25Mhz.

Searching around the web for some documentation and some include and
analyzing the uboot codeflow resulted in the divider being set wrongly
at /256 instead of /16 as the value was actually never set.
Applying the value restore the original load time for the Aquantia PHY.

This series mainly handle this by adding support for the "clock-frequency"
property.

Changes v2:
- Use DIV_ROUND_UP
- Introduce logic to chose a default value for 802.3 spec 2.5MHz

Christian Marangi (3):
dt-bindings: net: ipq4019-mdio: document now supported clock-frequency
net: mdio: ipq4019: add support for clock-frequency property
arm64: dts: qcom: ipq8074: add clock-frequency to MDIO node

.../bindings/net/qcom,ipq4019-mdio.yaml | 15 +++
arch/arm64/boot/dts/qcom/ipq8074.dtsi | 2 +
drivers/net/mdio/mdio-ipq4019.c | 109 +++++++++++++++++-
3 files changed, 120 insertions(+), 6 deletions(-)

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2.43.0