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

Manivannan Sadhasivam
2024-12-18T09:08:43Z

On Tue, Dec 17, 2024 at 10:48:43AM +0100, Christian Bruel wrote:
>
>
> 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
>

In that case, phy should be the clock provider to RCC and PCIe should get the
gated clock it.

- Mani

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