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

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 10.02.2025 4:09 AM, Yijie Yang wrote:
> 
> 
> On 2025-01-27 18:49, Konrad Dybcio wrote:
>> 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@quicinc.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.
> 
> But what about the out-of-tree boards that Andrew mentioned? We need to ensure we don't break them, right?

No. What's not on the list, doesn't exist

Konrad