[PATCH net v3 0/3] Fix broken link with TH1520 GMAC when linkspeed changes

[Yao Zi]

It's noted that on TH1520 SoC, the GMAC's link becomes broken after
the link speed is changed (for example, running ethtool -s eth0 speed
100 on the peer when negotiated to 1Gbps), but the GMAC could function
normally if the speed is brought back to the initial.

Just like many other SoCs utilizing STMMAC IP, we need to adjust the TX
clock supplying TH1520's GMAC through some SoC-specific glue registers
when linkspeed changes. But it's found that after the full kernel
startup, reading from them results in garbage and writing to them makes
no effect, which is the cause of broken link.

Further testing shows perisys-apb4-hclk must be ungated for normal
access to Th1520 GMAC APB glue registers, which is neither described in
dt-binding nor acquired by the driver.

This series expands the dt-binding of TH1520's GMAC to allow an extra
"APB glue registers interface clock", instructs the driver to acquire
and enable the clock, and finally supplies CLK_PERISYS_APB4_HCLK for
TH1520's GMACs in SoC devicetree.

Changed from v2
- dt-binding: Drop the Tested-by tag
- driver
  - Improve the commit message to mention the dt-compatibility problem
  - Add a comment about the dt-compatibility problem
  - Emit a warning when failed to get APB clock
  - Stop using the optional clock-getting API since it doesn't help much
    when we need to handle the missing case.
- Collect review tags
- Link to v2: https://lore.kernel.org/netdev/20250801091240.46114-1-ziyao@xxxxxxxxxxx/

Changed from v1
- Make apb clock essential in dt-binding
- Collect review tags
- Link to v1: https://lore.kernel.org/all/20250729093734.40132-1-ziyao@xxxxxxxxxxx/

Yao Zi (3):
  dt-bindings: net: thead,th1520-gmac: Describe APB interface clock
  net: stmmac: thead: Get and enable APB clock on initialization
  riscv: dts: thead: Add APB clocks for TH1520 GMACs

 .../devicetree/bindings/net/thead,th1520-gmac.yaml |  6 ++++--
 arch/riscv/boot/dts/thead/th1520.dtsi              | 10 ++++++----
 drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c  | 14 ++++++++++++++
 3 files changed, 24 insertions(+), 6 deletions(-)

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2.50.1