linux-kernel - Re: [PATCH v3 2/4] net: stmmac: dwmac-qcom-ethqos: Mask PHY mode if configured with rgmii-id

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Message-ID: <20250121141734.164ef891@device-291.home>
Date: Tue, 21 Jan 2025 14:17:34 +0100
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: Yijie Yang <quic_yijiyang@...cinc.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
 <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Rob Herring
 <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Vinod Koul <vkoul@...nel.org>, Maxime Coquelin
 <mcoquelin.stm32@...il.com>, Alexandre Torgue
 <alexandre.torgue@...s.st.com>, Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>, Richard Cochran
 <richardcochran@...il.com>, <netdev@...r.kernel.org>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <linux-arm-msm@...r.kernel.org>,
 <linux-stm32@...md-mailman.stormreply.com>,
 <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 2/4] net: stmmac: dwmac-qcom-ethqos: Mask PHY mode if
 configured with rgmii-id

Hi,

On Tue, 21 Jan 2025 15:54:54 +0800
Yijie Yang <quic_yijiyang@...cinc.com> wrote:

> The Qualcomm board always chooses the MAC to provide the delay instead of
> the PHY, which is completely opposite to the suggestion of the Linux
> kernel. The usage of phy-mode in legacy DTS was also incorrect. Change the
> phy_mode passed from the DTS to the driver from PHY_INTERFACE_MODE_RGMII_ID
> to PHY_INTERFACE_MODE_RGMII to ensure correct operation and adherence to
> the definition.
> To address the ABI compatibility issue between the kernel and DTS caused by
> this change, handle the compatible string 'qcom,qcs404-evb-4000' in the
> code, as it is the only legacy board that mistakenly uses the 'rgmii'
> phy-mode.
> 
> Signed-off-by: Yijie Yang <quic_yijiyang@...cinc.com>
> ---
>  .../net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c    | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
> index 2a5b38723635b5ef9233ca4709e99dd5ddf06b77..e228a62723e221d58d8c4f104109e0dcf682d06d 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
> @@ -401,14 +401,11 @@ static int ethqos_dll_configure(struct qcom_ethqos *ethqos)
>  static int ethqos_rgmii_macro_init(struct qcom_ethqos *ethqos)
>  {
>  	struct device *dev = &ethqos->pdev->dev;
> -	int phase_shift;
> +	int phase_shift = 0;
>  	int loopback;
>  
>  	/* Determine if the PHY adds a 2 ns TX delay or the MAC handles it */
> -	if (ethqos->phy_mode == PHY_INTERFACE_MODE_RGMII_ID ||
> -	    ethqos->phy_mode == PHY_INTERFACE_MODE_RGMII_TXID)
> -		phase_shift = 0;
> -	else
> +	if (ethqos->phy_mode == PHY_INTERFACE_MODE_RGMII_ID)
>  		phase_shift = RGMII_CONFIG2_TX_CLK_PHASE_SHIFT_EN;

So this looks like a driver modification to deal with errors in
devicetree, and these modifications don't seem to be correct.

You should set RGMII_CONFIG2_TX_CLK_PHASE_SHIFT_EN (i.e. adding a delay
n the TX line) when the PHY does not add internal delays on that line
(so, when the mode is rgmii or rgmii-rxid. The previous logic looks
correct in that regard.

Can you elaborate a bit more on the issue you are seeing ? On what
hardware is this happening ? What's the RGMII setup used (i.e. which
PHY, which mode, is there any delay lines on the PCB ?)

Thanks,

Maxime