PCI: imx6: Toggle the core reset for i.MX95 PCIe

Add toggling core reset for i.MX95 to align with PHY's power-up sequence.
Note that the register is named as IMX95_PCIE_COLD_RST in hardware, though
it is used to reset the PCIe core.

Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
[mani: subject and description rewording]
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20250416081314.3929794-4-hongxing.zhu@nxp.com

Author: Richard Zhu

drivers/pci/controller/dwc/pci-imx6.c

@@ -71,6 +71,9 @@
 #define IMX95_SID_MASK				GENMASK(5, 0)
 #define IMX95_MAX_LUT				32
 
+#define IMX95_PCIE_RST_CTRL			0x3010
+#define IMX95_PCIE_COLD_RST			BIT(0)
+
 #define to_imx_pcie(x)	dev_get_drvdata((x)->dev)
 
 enum imx_pcie_variants {
@@ -773,6 +776,43 @@ static int imx7d_pcie_core_reset(struct imx_pcie *imx_pcie, bool assert)
 	return 0;
 }
 
+static int imx95_pcie_core_reset(struct imx_pcie *imx_pcie, bool assert)
+{
+	u32 val;
+
+	if (assert) {
+		/*
+		 * From i.MX95 PCIe PHY perspective, the COLD reset toggle
+		 * should be complete after power-up by the following sequence.
+		 *                 > 10us(at power-up)
+		 *                 > 10ns(warm reset)
+		 *               |<------------>|
+		 *                ______________
+		 * phy_reset ____/              \________________
+		 *                                   ____________
+		 * ref_clk_en_______________________/
+		 * Toggle COLD reset aligned with this sequence for i.MX95 PCIe.
+		 */
+		regmap_set_bits(imx_pcie->iomuxc_gpr, IMX95_PCIE_RST_CTRL,
+				IMX95_PCIE_COLD_RST);
+		/*
+		 * Make sure the write to IMX95_PCIE_RST_CTRL is flushed to the
+		 * hardware by doing a read. Otherwise, there is no guarantee
+		 * that the write has reached the hardware before udelay().
+		 */
+		regmap_read_bypassed(imx_pcie->iomuxc_gpr, IMX95_PCIE_RST_CTRL,
+				     &val);
+		udelay(15);
+		regmap_clear_bits(imx_pcie->iomuxc_gpr, IMX95_PCIE_RST_CTRL,
+				  IMX95_PCIE_COLD_RST);
+		regmap_read_bypassed(imx_pcie->iomuxc_gpr, IMX95_PCIE_RST_CTRL,
+				     &val);
+		udelay(10);
+	}
+
+	return 0;
+}
+
 static void imx_pcie_assert_core_reset(struct imx_pcie *imx_pcie)
 {
 	reset_control_assert(imx_pcie->pciephy_reset);
@@ -1739,6 +1779,7 @@ static const struct imx_pcie_drvdata drvdata[] = {
 		.ltssm_mask = IMX95_PCIE_LTSSM_EN,
 		.mode_off[0]  = IMX95_PE0_GEN_CTRL_1,
 		.mode_mask[0] = IMX95_PCIE_DEVICE_TYPE,
+		.core_reset = imx95_pcie_core_reset,
 		.init_phy = imx95_pcie_init_phy,
 	},
 	[IMX8MQ_EP] = {
@@ -1792,6 +1833,7 @@ static const struct imx_pcie_drvdata drvdata[] = {
 		.mode_off[0]  = IMX95_PE0_GEN_CTRL_1,
 		.mode_mask[0] = IMX95_PCIE_DEVICE_TYPE,
 		.init_phy = imx95_pcie_init_phy,
+		.core_reset = imx95_pcie_core_reset,
 		.epc_features = &imx95_pcie_epc_features,
 		.mode = DW_PCIE_EP_TYPE,
 	},