dwc_eth_qos driver for tegra

[Rasmus Villemoes]

On 23/05/2022 12.57, Marek Vasut wrote:
> On 5/23/22 11:17, Rasmus Villemoes wrote:
>> Hi
> 
> Hi,
> 
>> I'm looking at switching the dwc_eth_qos driver over to use
>> dm_eth_phy_connect(). However, I'm a little puzzled by the code for the
>> tegra variant. The comment at the top of the file, as well as
>> tegra186.dtsi, says
>>
>>    phy-mode = "rgmii";
>>
>> But eqos_get_interface_tegra186() returns a hard-coded
>> PHY_INTERFACE_MODE_MII. Now the commit which introduced the ->interface
>> abstraction, ac2d4efb16e (net: dwc_eth_qos: add Ethernet stm32mp1
>> support), and that eqos_get_interface_tegra186() function, changed
>>
>> -       eqos->phy = phy_connect(eqos->mii, 0, dev, 0);
>>
>> to
>>
>> +               eqos->phy = phy_connect(eqos->mii, 0, dev,
>> +                                       eqos->config->interface(dev));
>>
>> and that last hard-coded 0 in the former phy_connect() is indeed
>> equivalent to PHY_INTERFACE_MODE_MII.
>>
>> So which is it? It would be nice if one could just rely on
>> dm_eth_phy_connect() picking up the correct value from device tree, and
>> drop all the code which duplicates parsing of phy-mode from the ethernet
>> driver.
> 
> linux-2.6$ git grep mii arch/arm64/boot/dts/nvidia/tegra186*
> arch/arm64/boot/dts/nvidia/tegra186-p3310.dtsi:         phy-mode = "rgmii";
> arch/arm64/boot/dts/nvidia/tegra186-p3509-0000+p3636-0001.dts: phy-mode
> = "rgmii-id";
> 
> So probably RGMII ?

Well, yes, I also did check the linux device tree files which also says
rgmii, but that doesn't explain why the U-Boot driver code seems to
ignore that entirely and use mii hardcoded, both before and after
ac2d4efb16e.

So another way of asking: does this driver actually work today, and/or
has it worked at some point? I assume the answer is yes - after all, the
very first commit "supports the specific configuration used in NVIDIA's
Tegra186 chip", but that commit also did that phy_connect() with a last
argument of 0 aka PHY_INTERFACE_MODE_MII.

And would it break if one started taking the phy-mode from device tree?
If so, should device tree be updated to say "mii"?

Rasmus