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

[Marek Vasut <marex@denx.de>]

On 6/18/24 11:09 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 ?

> (you can 
> see than diviser are only for RMII mode)

Do you refer to /2 and /20 dividers to the left of mac_speed_o[0] ?