netdev - Re: [PATCH net-next] net: stmmac: qcom-ethqos: remove MAC_CTRL

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Message-ID: <bb2865b6-6c17-49e4-b18f-b9baad771830@oss.qualcomm.com>
Date: Thu, 30 Oct 2025 14:08:41 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>,
        Mohd Ayaan Anwar <mohd.anwar@....qualcomm.com>
Cc: Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Andrew Lunn <andrew+netdev@...n.ch>,
        "David S. Miller"
 <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        Maxime Coquelin <mcoquelin.stm32@...il.com>, netdev@...r.kernel.org,
        Paolo Abeni <pabeni@...hat.com>, Vinod Koul <vkoul@...nel.org>
Subject: Re: [PATCH net-next] net: stmmac: qcom-ethqos: remove MAC_CTRL_REG
 modification

On 10/30/25 1:17 PM, Russell King (Oracle) wrote:
> Konrad, Ayaan,
> 
> Can you shed any light on the manipulation of the RGMII_IO_MACRO_CONFIG
> and RGMII_IO_MACRO_CONFIG2 registers in ethqos_configure_sgmii()?
> 
> Specifically:
> - why would RGMII_CONFIG2_RGMII_CLK_SEL_CFG be set for 2.5G and 1G
>   speeds, but never be cleared for any other speed?

BIT(16) - "enable to transmit delayed clock in RGMII 100/10 ID Mode"

> - why is RGMII_CONFIG_SGMII_CLK_DVDR set to SGMII_10M_RX_CLK_DVDR
>   for 10M, but never set to any other value for other speeds?

[18:10] - In short, it configures a divider. The expected value is 0x13
for 10 Mbps / RMII mode

which seems to have been problematic given:

https://lore.kernel.org/all/20231212092208.22393-1-quic_snehshah@quicinc.com/

But it didn't say what hardware had this issue.. whether it concerns a
specific SoC or all of them..

A programming guide mentions the new 0x31 value for 10 Mbps in a
SoC-common paragraph so I suppose it's indeed better-er.. Perhaps issues
could arise if you switch back to a faster mode?
> To me, this code looks very suspicious.
> 
> If you have time, please test with a connection capable of 1000BASE-T,
> 100BASE-TX and 10BASE-T, modifying the advertisement to make it
> negotiate each of these, and checking that packet transfer is still
> possible.

No HW with an ethernet port at hand, sorry

Konrad