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

[Christophe ROULLIER <christophe.roullier@foss.st.com>]

Hi Marek,

On 6/18/24 17:00, Marek Vasut wrote:
> 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 ?

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). 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.

>
>> (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] ?