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

From: Konrad Dybcio
Date: Mon Jan 27 2025 - 05:49:56 EST


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@xxxxxxxxxxx>
>>>> ---
>>>> .../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