[PATCH net-next v4] net: stmmac: dwmac-qcom-ethqos: Add support for 2.5G SGMII

[Sneh Shah]

On 2/13/2024 7:00 AM, Jakub Kicinski wrote:
> On Thu,  8 Feb 2024 16:47:14 +0530 Sneh Shah wrote:
>> Serdes phy needs to operate at 2500 mode for 2.5G speed and 1000
>> mode for 1G/100M/10M speed.
>> Added changes to configure serdes phy and mac based on link speed.
>> Changing serdes phy speed involves multiple register writes for
>> serdes block. To avoid redundant write operations only update serdes
>> phy when new speed is different.
> 
> Sounds like 2 separate changes in one patch, please split the
> optimization of not writing the registers multiple times and
> the 2.5G support.
> 

Optimization is part of 2.5G support change only. with introduction of
2.5G speed support we need to update reconfigure serdes phy. there are
2 different serdes configs.
1. config for 2.5G
2. common config 1G/100M/10M

The change here is not to reconfigure serdes phy among
1G/100M/10M speeds and only reconfigure if it switches to 2.5G.

>> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
>> index 31631e3f89d0..6bbdbb7bef44 100644
>> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
>> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
>> @@ -106,6 +106,7 @@ struct qcom_ethqos {
>>  	struct clk *link_clk;
>>  	struct phy *serdes_phy;
>>  	unsigned int speed;
>> +	int serdes_speed;
> 
> Why signed if speed itself is unsigned?

In stmmac speed can be assigned as SPEED_UNKNOWN which will be -1.
I will fix speed being unsigned int in a separate patch.

> 
>>  	/* Enable and restart the Auto-Negotiation */
>>  	if (ane)
>>  		value |= GMAC_AN_CTRL_ANE | GMAC_AN_CTRL_RAN;
>> +	else
>> +		value &= ~GMAC_AN_CTRL_ANE;
> 
> That looks unrelated. Either a separate patch or please explain in the
> commit msg why.

For 2.5G speed support MAC PCS autoneg needs to be disabled.
This adds the change to disable PCS autoneg. I will update commit
message to add more dtails