-----Original Message-----
From: Manivannan Sadhasivam <mani@kernel.org>
Sent: 2025年9月22日 14:13
To: Hongxing Zhu <hongxing.zhu@nxp.com>
Cc: Frank Li <frank.li@nxp.com>; jingoohan1@gmail.com;
l.stach@pengutronix.de; lpieralisi@kernel.org; kwilczynski@kernel.org;
robh@kernel.org; bhelgaas@google.com; shawnguo@kernel.org;
s.hauer@pengutronix.de; kernel@pengutronix.de; festevam@gmail.com;
linux-pci@vger.kernel.org; linux-arm-kernel@lists.infradead.org;
imx@lists.linux.dev; linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 2/2] PCI: imx6: Add a method to handle CLKREQ#
override active low

On Mon, Sep 22, 2025 at 10:37:41AM +0800, Richard Zhu wrote:

quoted

The CLKREQ# is an open drain, active low signal that is driven low by
the card to request reference clock. It's an optional signal added in
PCIe CEM r4.0, sec 2. Thus, this signal wouldn't be driven low if it's
reserved.

Since the reference clock controlled by CLKREQ# may be required by
i.MX PCIe host too. To make sure this clock is ready even when the
CLKREQ# isn't driven low by the card(e.x the scenario described
above), force CLKREQ# override active low for i.MX PCIe host during

initialization.

quoted

The CLKREQ# override can be cleared safely when supports-clkreq is
present and PCIe link is up later. Because the CLKREQ# would be driven
low by the card at this time.

Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
---
 drivers/pci/controller/dwc/pci-imx6.c | 35
+++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/drivers/pci/controller/dwc/pci-imx6.c

b/drivers/pci/controller/dwc/pci-imx6.c
index 80e48746bbaf..a73632b47e2d 100644

--- a/drivers/pci/controller/dwc/pci-imx6.c
+++ b/drivers/pci/controller/dwc/pci-imx6.c

@@ -52,6 +52,8 @@
 #define IMX95_PCIE_REF_CLKEN			BIT(23)
 #define IMX95_PCIE_PHY_CR_PARA_SEL		BIT(9)
 #define IMX95_PCIE_SS_RW_REG_1			0xf4
+#define IMX95_PCIE_CLKREQ_OVERRIDE_EN		BIT(8)
+#define IMX95_PCIE_CLKREQ_OVERRIDE_VAL		BIT(9)
 #define IMX95_PCIE_SYS_AUX_PWR_DET		BIT(31)

 #define IMX95_PE0_GEN_CTRL_1			0x1050

@@ -136,6 +138,7 @@ struct imx_pcie_drvdata {
 	int (*enable_ref_clk)(struct imx_pcie *pcie, bool enable);
 	int (*core_reset)(struct imx_pcie *pcie, bool assert);
 	int (*wait_pll_lock)(struct imx_pcie *pcie);
+	void (*clr_clkreq_override)(struct imx_pcie *pcie);
 	const struct dw_pcie_host_ops *ops;
 };

@@ -149,6 +152,7 @@ struct imx_pcie {
 	struct gpio_desc	*reset_gpiod;
 	struct clk_bulk_data	*clks;
 	int			num_clks;
+	bool			supports_clkreq;
 	struct regmap		*iomuxc_gpr;
 	u16			msi_ctrl;
 	u32			controller_id;

@@ -267,6 +271,13 @@ static int imx95_pcie_init_phy(struct imx_pcie

*imx_pcie)

quoted

 			   IMX95_PCIE_REF_CLKEN,
 			   IMX95_PCIE_REF_CLKEN);

+	/* Force CLKREQ# low by override */
+	regmap_update_bits(imx_pcie->iomuxc_gpr,
+			   IMX95_PCIE_SS_RW_REG_1,
+			   IMX95_PCIE_CLKREQ_OVERRIDE_EN |
+			   IMX95_PCIE_CLKREQ_OVERRIDE_VAL,
+			   IMX95_PCIE_CLKREQ_OVERRIDE_EN |
+			   IMX95_PCIE_CLKREQ_OVERRIDE_VAL);

This should be:

	imx95_pcie_clkreq_override(imx_pcie, true);

refer below...

quoted

 	return 0;
 }

@@ -1298,6 +1309,18 @@ static void imx_pcie_host_exit(struct dw_pcie_rp

*pp)

quoted

 		regulator_disable(imx_pcie->vpcie);
 }

+static void imx8mm_pcie_clr_clkreq_override(struct imx_pcie
+*imx_pcie) {
+	imx8mm_pcie_enable_ref_clk(imx_pcie, false);

Just noticed this discrepancy. 'imx8mm_pcie_enable_ref_clk(, false)' is
enabling the CLKREQ# override, thereby enabling the refclk. But only for
imx8mm, this helper is called as imx8mm_pcie_enable_ref_clk(). But for
imx95, the equivalent function is called as imx95_pcie_clr_clkreq_override().
This is causing confusion.

Maybe you should just call both functions as:

	imx8mm_pcie_clkreq_override(imx_pcie, bool enable);
	imx95_pcie_clkreq_override(imx_pcie, bool enable);

Then,

	imx8mm_pcie_clr_clkreq_override(struct imx_pcie *imx_pcie)
	{
		imx8mm_pcie_clkreq_override(imx_pcie, false)
	}

	imx95_pcie_clr_clkreq_override(struct imx_pcie *imx_pcie)
	{
		imx95_pcie_clkreq_override(imx_pcie, false)
	}

and populate the clr_clkreq_override() callback.

Good proposal, let me clean up codes as this.
Thanks.

Best Regards
Richard Zhu

- Mani

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