Re: [PATCH v2 4/5] PCI: stm32: Add PCIe endpoint support for STM32MP25

Christian Bruel
2024-12-17T10:09:35Z

On 12/16/24 17:17, Manivannan Sadhasivam wrote:
> On Mon, Dec 16, 2024 at 11:02:07AM +0100, Christian Bruel wrote:
>> Hi Manivanna,
>>
>> On 12/3/24 16:22, Manivannan Sadhasivam wrote:
>>> On Tue, Nov 26, 2024 at 04:51:18PM +0100, Christian Bruel wrote:
>>>
>>> [...]
>>>
>>>> +static int stm32_pcie_start_link(struct dw_pcie *pci)
>>>> +{
>>>> + struct stm32_pcie *stm32_pcie = to_stm32_pcie(pci);
>>>> + int ret;
>>>> +
>>>> + if (stm32_pcie->link_status == STM32_PCIE_EP_LINK_ENABLED) {
>>>> + dev_dbg(pci->dev, "Link is already enabled\n");
>>>> + return 0;
>>>> + }
>>>> +
>>>> + ret = stm32_pcie_enable_link(pci);
>>>> + if (ret) {
>>>> + dev_err(pci->dev, "PCIe cannot establish link: %d\n", ret);
>>>> + return ret;
>>>> + }
>>>
>>> How the REFCLK is supplied to the endpoint? From host or generated locally?
>>
>> From Host only, we don't support the separated clock model.
>>
>
> OK. So even without refclk you are still able to access the controller
> registers? So the controller CSRs should be accessible by separate local clock I
> believe.
>
> Anyhow, please add this limitation (refclk dependency from host) in commit
> message.
>
> [...]
>
>>>> + ret = phy_set_mode(stm32_pcie->phy, PHY_MODE_PCIE);
>>>
>>> Hmm, so PHY mode is common for both endpoint and host?
>>
>> Yes it is. We need to init the phy here because it is a clock source for the
>> PCIe core clk
>>
>
> Clock source? Is it coming directly to PCIe or through RCC? There is no direct
> clock representation from PHY to PCIe in DT binding.

The core_clk is generated directly by the PLL in the COMBOPHY, gated by
the RCC

>
> - Mani
>