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

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Message-ID: <20241218090834.bz5htywl3sjbzq6w@thinkpad>
Date: Wed, 18 Dec 2024 14:38:34 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Christian Bruel <christian.bruel@...s.st.com>
Cc: lpieralisi@...nel.org, kw@...ux.com, robh@...nel.org,
	bhelgaas@...gle.com, krzk+dt@...nel.org, conor+dt@...nel.org,
	mcoquelin.stm32@...il.com, alexandre.torgue@...s.st.com,
	p.zabel@...gutronix.de, cassel@...nel.org,
	quic_schintav@...cinc.com, fabrice.gasnier@...s.st.com,
	linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/5] PCI: stm32: Add PCIe endpoint support for
 STM32MP25

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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