Re: [net-next,PATCH 2/2] net: stmmac: dwmac-stm32: stm32: add management of stm32mp25 for stm32

[Marek Vasut <marex@denx.de>]

On 6/19/24 9:41 AM, Christophe ROULLIER wrote:

Hi,

>>>>>>> +static int stm32mp2_configure_syscfg(struct plat_stmmacenet_data 
>>>>>>> *plat_dat)
>>>>>>> +{
>>>>>>> +    struct stm32_dwmac *dwmac = plat_dat->bsp_priv;
>>>>>>> +    u32 reg = dwmac->mode_reg;
>>>>>>> +    int val = 0;
>>>>>>> +
>>>>>>> +    switch (plat_dat->mac_interface) {
>>>>>>> +    case PHY_INTERFACE_MODE_MII:
>>>>>>> +        break;
>>>>>>
>>>>>> dwmac->enable_eth_ck does not apply to MII mode ? Why ?
>>>>>
>>>>> It is like MP1 and MP13, nothing to set in syscfg register for case 
>>>>> MII mode wo crystal.
>>>>
>>>> Have a look at STM32MP15xx RM0436 Figure 83. Peripheral clock 
>>>> distribution for Ethernet.
>>>>
>>>> If RCC (top-left corner of the figure) generates 25 MHz MII clock 
>>>> (yellow line) on eth_clk_fb (top-right corner), can I set 
>>>> ETH_REF_CLK_SEL to position '1' and ETH_SEL[2] to '0' and feed ETH 
>>>> (right side) clk_rx_i input with 25 MHz clock that way ?
>>>>
>>>> I seems like this should be possible, at least theoretically. Can 
>>>> you check with the hardware/silicon people ?
>>> No it is not possible (it will work if speed (and frequency) is fixed 
>>> 25Mhz=100Mbps, but for speed 10Mbps (2,5MHz) it will not work.
>>
>> Could the pll4_p_ck or pll3_q_ck generate either 25 MHz or 2.5 MHz as 
>> needed in that case ? Then it would work, right ?
> 
> Yes you can set frequency you want for pll4 or pll3, if you set 25MHz 
> and auto-negotiation of speed is 100Mbps it should work (pad ETH_CK of 
> 25MHz clock the PHY and eth_clk_fb set to 25MHz for clk_RX)
> 
> but if autoneg of speed is 10Mbps, then 2.5MHz is needed for clk_RX (you 
> will provide 25Mhz)

What if:

- Aneg is 10 Mbps
- PLL4_P_CK/PLL3_Q_CK = 2.5 MHz
- ETH_REF_CLK_SEL = 1
- ETH_SEL[2] = 0

?

Then, clk_rx_i is 2.5 MHz, right ?

Does this configuration work ?

> . For RMII case, frequency from pll (eth_clk_fb) is 
> automatically adjust in function of speed value, thanks to diviser /2, 
> /20 with mac_speed_o.