[PATCH v2 2/2] PCI: imx6: Assert ref_clk_en after reference clock stabilizes on i.MX95

[Richard Zhu]

According to the PHY Databook Common Block Signals section, the
ref_clk_en signal must remain de-asserted until the reference clock is
running at the appropriate frequency. Once the clock is stable,
ref_clk_en can be asserted. For lower power states where the reference
clock to the PHY is disabled, ref_clk_en should also be de-asserted.

Move the ref_clk_en bit manipulation into imx95_pcie_enable_ref_clk()
to ensure the reference clock stabilizes before ref_clk_en is asserted
and before the PHY reset is de-asserted. This aligns with the timing
requirements specified in the PHY documentation.

Fixes: d8574ce57d76 ("PCI: imx6: Add external reference clock input mode support")
Cc: <stable at vger.kernel.org>
Signed-off-by: Richard Zhu <hongxing.zhu at nxp.com>
---
 drivers/pci/controller/dwc/pci-imx6.c | 28 +++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
index 66e760015c92..c4b079c93648 100644
--- a/drivers/pci/controller/dwc/pci-imx6.c
+++ b/drivers/pci/controller/dwc/pci-imx6.c
@@ -270,8 +270,6 @@ static int imx95_pcie_init_pre_reset(struct imx_pcie *imx_pcie)
 
 static int imx95_pcie_init_phy(struct imx_pcie *imx_pcie)
 {
-	bool ext = imx_pcie->enable_ext_refclk;
-
 	/*
 	 * ERR051624: The Controller Without Vaux Cannot Exit L23 Ready
 	 * Through Beacon or PERST# De-assertion
@@ -290,10 +288,6 @@ static int imx95_pcie_init_phy(struct imx_pcie *imx_pcie)
 			IMX95_PCIE_PHY_CR_PARA_SEL,
 			IMX95_PCIE_PHY_CR_PARA_SEL);
 
-	regmap_update_bits(imx_pcie->iomuxc_gpr, IMX95_PCIE_SS_RW_REG_0,
-			   IMX95_PCIE_REF_CLKEN,
-			   ext ? 0 : IMX95_PCIE_REF_CLKEN);
-
 	return 0;
 }
 
@@ -742,7 +736,29 @@ static void imx95_pcie_clkreq_override(struct imx_pcie *imx_pcie, bool enable)
 
 static int imx95_pcie_enable_ref_clk(struct imx_pcie *imx_pcie, bool enable)
 {
+	bool ext = imx_pcie->enable_ext_refclk;
+
 	imx95_pcie_clkreq_override(imx_pcie, enable);
+	/*
+	 * The ref_clk_en signal must remain de-asserted until the
+	 * reference clock is running at appropriate frequency, at which
+	 * point this bit can be asserted. For lower power states where
+	 * the reference clock to the PHY is disabled, it may also be
+	 * de-asserted.
+	 * +------------------- -+--------+----------------+
+	 * | External clock mode | Enable | PCIE_REF_CLKEN |
+	 * +---------------------+--------+----------------+
+	 * | TRUE                | X      | 1b'0           |
+	 * +---------------------+--------+----------------+
+	 * | FALSE               | TRUE   | 1b'1           |
+	 * +---------------------+--------+----------------+
+	 * | FALSE               | FALSE  | 1b'0           |
+	 * +---------------------+--------+----------------+
+	 */
+	regmap_update_bits(imx_pcie->iomuxc_gpr, IMX95_PCIE_SS_RW_REG_0,
+			   IMX95_PCIE_REF_CLKEN,
+			   ext || !enable ? 0 : IMX95_PCIE_REF_CLKEN);
+
 	return 0;
 }
 
-- 
2.37.1