[PATCH v7 4/4] PCI: dwc: Add support for configuring lane equalization presets

[Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>]

PCIe equalization presets are predefined settings used to optimize
signal integrity by compensating for signal loss and distortion in
high-speed data transmission.

Based upon the number of lanes and the data rate supported, write
the preset data read from the device tree in to the lane equalization
control registers.

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
---
 drivers/pci/controller/dwc/pcie-designware-host.c | 66 +++++++++++++++++++++++
 drivers/pci/controller/dwc/pcie-designware.h      |  3 ++
 include/uapi/linux/pci_regs.h                     |  3 ++
 3 files changed, 72 insertions(+)

diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index dd56cc02f4ef..ea596119de92 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c
@@ -507,6 +507,10 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
 	if (pci->num_lanes < 1)
 		pci->num_lanes = dw_pcie_link_get_max_link_width(pci);
 
+	ret = of_pci_get_equalization_presets(dev, &pp->presets, pci->num_lanes);
+	if (ret)
+		goto err_free_msi;
+
 	/*
 	 * Allocate the resource for MSG TLP before programming the iATU
 	 * outbound window in dw_pcie_setup_rc(). Since the allocation depends
@@ -808,6 +812,67 @@ static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
 	return 0;
 }
 
+static void dw_pcie_program_presets(struct dw_pcie_rp *pp, enum pci_bus_speed speed)
+{
+	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
+	u8 lane_eq_offset, lane_reg_size, cap_id;
+	u8 *presets;
+	u32 cap;
+	int i;
+
+	if (speed == PCIE_SPEED_8_0GT) {
+		presets = (u8 *)pp->presets.eq_presets_8gts;
+		lane_eq_offset =  PCI_SECPCI_LE_CTRL;
+		cap_id = PCI_EXT_CAP_ID_SECPCI;
+		/* For data rate of 8 GT/S each lane equalization control is 16bits wide*/
+		lane_reg_size = 0x2;
+	} else if (speed == PCIE_SPEED_16_0GT) {
+		presets = pp->presets.eq_presets_Ngts[EQ_PRESET_TYPE_16GTS];
+		lane_eq_offset = PCI_PL_16GT_LE_CTRL;
+		cap_id = PCI_EXT_CAP_ID_PL_16GT;
+		lane_reg_size = 0x1;
+	} else {
+		dev_WARN_ONCE(pci->dev, 1, "Not supported data rate %s\n",
+			      pci_speed_string(speed));
+		return;
+	}
+
+	if (presets[0] == PCI_EQ_RESV) {
+		dev_WARN_ONCE(pci->dev, 1,
+			      "Lane equalization preset properties are missing for %s\n",
+			      pci_speed_string(speed));
+		return;
+	}
+
+	cap = dw_pcie_find_ext_capability(pci, cap_id);
+	if (!cap)
+		return;
+
+	/*
+	 * Write preset values to the registers byte-by-byte for the given
+	 * number of lanes and register size.
+	 */
+	for (i = 0; i < pci->num_lanes * lane_reg_size; i++)
+		dw_pcie_writeb_dbi(pci, cap + lane_eq_offset + i, presets[i]);
+}
+
+static void dw_pcie_config_presets(struct dw_pcie_rp *pp)
+{
+	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
+	enum pci_bus_speed speed = pcie_link_speed[pci->max_link_speed];
+
+	/*
+	 * Lane equalization needs to be perfomed for all data rates
+	 * the controller supports and for all supported lanes.
+	 */
+
+	if (speed >= PCIE_SPEED_8_0GT)
+		dw_pcie_program_presets(pp, PCIE_SPEED_8_0GT);
+
+	if (speed >= PCIE_SPEED_16_0GT)
+		dw_pcie_program_presets(pp, PCIE_SPEED_16_0GT);
+}
+
 int dw_pcie_setup_rc(struct dw_pcie_rp *pp)
 {
 	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
@@ -861,6 +926,7 @@ int dw_pcie_setup_rc(struct dw_pcie_rp *pp)
 		PCI_COMMAND_MASTER | PCI_COMMAND_SERR;
 	dw_pcie_writel_dbi(pci, PCI_COMMAND, val);
 
+	dw_pcie_config_presets(pp);
 	/*
 	 * If the platform provides its own child bus config accesses, it means
 	 * the platform uses its own address translation component rather than
diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
index 61d1fb6b437b..30ae8d3f4282 100644
--- a/drivers/pci/controller/dwc/pcie-designware.h
+++ b/drivers/pci/controller/dwc/pcie-designware.h
@@ -25,6 +25,8 @@
 #include <linux/pci-epc.h>
 #include <linux/pci-epf.h>
 
+#include "../../pci.h"
+
 /* DWC PCIe IP-core versions (native support since v4.70a) */
 #define DW_PCIE_VER_365A		0x3336352a
 #define DW_PCIE_VER_460A		0x3436302a
@@ -381,6 +383,7 @@ struct dw_pcie_rp {
 	int			msg_atu_index;
 	struct resource		*msg_res;
 	bool			use_linkup_irq;
+	struct pci_eq_presets	presets;
 };
 
 struct dw_pcie_ep_ops {
diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
index 3445c4970e4d..2cd20170adb4 100644
--- a/include/uapi/linux/pci_regs.h
+++ b/include/uapi/linux/pci_regs.h
@@ -1140,6 +1140,9 @@
 #define PCI_DLF_CAP		0x04	/* Capabilities Register */
 #define  PCI_DLF_EXCHANGE_ENABLE	0x80000000  /* Data Link Feature Exchange Enable */
 
+/* Secondary PCIe Capability 8.0 GT/s */
+#define PCI_SECPCI_LE_CTRL	0x0c /* Lane Equalization Control Register */
+
 /* Physical Layer 16.0 GT/s */
 #define PCI_PL_16GT_LE_CTRL	0x20	/* Lane Equalization Control Register */
 #define  PCI_PL_16GT_LE_CTRL_DSP_TX_PRESET_MASK		0x0000000F

-- 
2.34.1