Re: [PATCH net-next v4 1/3] dt-bindings: ethernet: eswin: add clock sampling control

[Conor Dooley <conor@kernel.org>]

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On Fri, Mar 13, 2026 at 03:53:51PM +0800, lizhi2@eswincomputing.com wrote:
> From: Zhi Li <lizhi2@eswincomputing.com>
> 
> Due to chip backend reasons, there is already an approximately 4-5 ns
> skew between the RX clock and data of the eth1 MAC controller inside
> the silicon.
> 
> For 1000M, the RX clock must be inverted since it is not possible to
> meet the RGMII timing requirements using only rx-internal-delay-ps on
> the MAC together with the standard 2 ns delay on the PHY. Therefore,
> even on a properly designed board, eth1 still requires RX clock
> inversion.
> 
> This behaviour effectively breaks the RGMII timing assumptions at the
> SoC level.
> 
> For the TX path of eth1, there is also a skew between the TX clock
> and data on the MAC controller inside the silicon. This skew happens
> to be approximately 2 ns. Therefore, it can be considered that the
> 2 ns delay of TX is provided by the MAC, so the TX is compliant with
> the RGMII standard.
> 
> For 10/100 operation, the approximately 4-5 ns skew in the chip does
> not break the standard. The RGMII timing table (Section 3.3) specifies
> that for 10/100 operation the maximum value is unspecified:
> https://community.nxp.com/pwmxy87654/attachments/pwmxy87654/imx-processors/20655/1/RGMIIv2_0_final_hp.pdf
> 
> Due to the eth1 silicon behavior described above, a new compatible
> string "eswin,eic7700-qos-eth-clk-inversion" is added to the device
> tree. This allows the driver to handle the differences between eth1
> and eth0 through dedicated logic.
> 
> The rx-internal-delay-ps and tx-internal-delay-ps properties now use
> minimum and maximum constraints to reflect the actual hardware delay
> range (0-2540 ps) applied in 20 ps steps. This relaxes the binding
> validation compared to the previous enum-based definition and avoids
> regressions for existing DTBs while keeping the same hardware limits.
> 
> Treat the RX/TX internal delay properties as optional, board-specific
> tuning knobs and remove them from the example to avoid encouraging
> their use.
> 
> In addition, the binding now includes additional background information
> about the HSP CSR registers accessed by the MAC. The TXD and RXD delay
> control registers are included so the driver can explicitly clear any
> residual configuration left by the bootloader.
> 
> Background reference for the High-Speed Subsystem and HSP CSR block is
> available in Chapter 10 ("High-Speed Interface") of the EIC7700X SoC
> Technical Reference Manual, Part 4
> (EIC7700X_SoC_Technical_Reference_Manual_Part4.pdf):
> https://github.com/eswincomputing/EIC7700X-SoC-Technical-Reference-Manual/releases
> 
> There are currently no in-tree users of the EIC7700 Ethernet driver, so
> these changes are safe.
> 
> Fixes: 888bd0eca93c ("dt-bindings: ethernet: eswin: Document for EIC7700 SoC")
> Signed-off-by: Zhi Li <lizhi2@eswincomputing.com>

Krzysztof might not yet be happy with the compatible naming, but from my
pov:
Acked-by: Conor Dooley <conor.dooley@microchip.com>

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