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: <71da0edf-9b2a-464e-8979-8e09f7828120@oss.qualcomm.com>
Date: Mon, 27 Jan 2025 11:49:34 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Krzysztof Kozlowski <krzk@...nel.org>,
        Yijie Yang <quic_yijiyang@...cinc.com>,
        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>
Cc: 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

On 22.01.2025 10:48 AM, Krzysztof Kozlowski wrote:
> On 22/01/2025 09:56, Yijie Yang wrote:
>>
>>
>> On 2025-01-21 20:47, Krzysztof Kozlowski wrote:
>>> On 21/01/2025 08:54, Yijie Yang 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.
>>>
>>>
>>> How does the Linux kernel suggest it?
>>>
>>>> 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;
>>>>   
>>>>   	/* Disable loopback mode */
>>>> @@ -810,6 +807,17 @@ static int qcom_ethqos_probe(struct platform_device *pdev)
>>>>   	ret = of_get_phy_mode(np, &ethqos->phy_mode);
>>>>   	if (ret)
>>>>   		return dev_err_probe(dev, ret, "Failed to get phy mode\n");
>>>> +
>>>> +	root = of_find_node_by_path("/");
>>>> +	if (root && of_device_is_compatible(root, "qcom,qcs404-evb-4000"))
>>>
>>>
>>> First, just check if machine is compatible, don't open code it.
>>>
>>> Second, drivers should really, really not rely on the machine. I don't
>>> think how this resolves ABI break for other users at all.
>>
>> As detailed in the commit description, some boards mistakenly use the 
>> 'rgmii' phy-mode, and the MAC driver has also incorrectly parsed and 
> 
> That's a kind of an ABI now, assuming it worked fine.

I'm inclined to think it's better to drop compatibility given we're talking
about rather obscure boards here.

$ rg 'mode.*=.*"rgmii"' arch/arm64/boot/dts/qcom -l

arch/arm64/boot/dts/qcom/sa8155p-adp.dts
arch/arm64/boot/dts/qcom/qcs404-evb-4000.dts

QCS404 seems to have zero interest from anyone (and has been considered
for removal upstream..).

The ADP doesn't see much traction either, last time around someone found
a boot breaking issue months after it was committed.

Konrad