[PATCH v3 4/4] PCI: dwc: Add support for configuring lane equalization presets

[Krishna Chaitanya Chundru]

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, read the
devicetree property and write it in to the lane equalization control
registers.

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@xxxxxxxxxxxxxxxx>
---
 drivers/pci/controller/dwc/pcie-designware-host.c | 39 +++++++++++++++++++++++
 drivers/pci/controller/dwc/pcie-designware.h      |  3 ++
 include/uapi/linux/pci_regs.h                     |  3 ++
 3 files changed, 45 insertions(+)

diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index 2cd0acbf9e18..22d3d350918e 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
@@ -802,6 +806,40 @@ static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
 	return 0;
 }
 
+static void dw_pcie_program_presets(struct dw_pcie *pci, u8 cap_id, u8 lane_eq_offset,
+				    u8 lane_reg_size, u8 *presets, u8 num_lanes)
+{
+	u32 cap;
+	int i;
+
+	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 < 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];
+
+	/* For data rate of 8 GT/S each lane equalization control is 16bits wide */
+	if (speed >= PCIE_SPEED_8_0GT && pp->presets.eq_presets_8gts)
+		dw_pcie_program_presets(pci, PCI_EXT_CAP_ID_SECPCI, PCI_SECPCI_LE_CTRL,
+					0x2, pp->presets.eq_presets_8gts, pci->num_lanes);
+
+	/* For data rate of 16 GT/S each lane equalization control is 8bits wide */
+	if (speed >= PCIE_SPEED_16_0GT && pp->presets.eq_presets_16gts)
+		dw_pcie_program_presets(pci, PCI_EXT_CAP_ID_PL_16GT, PCI_PL_16GT_LE_CTRL,
+					0x1, pp->presets.eq_presets_16gts, pci->num_lanes);
+}
+
 int dw_pcie_setup_rc(struct dw_pcie_rp *pp)
 {
 	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
@@ -855,6 +893,7 @@ 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 500e793c9361..b12b33944df4 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
@@ -379,6 +381,7 @@ struct dw_pcie_rp {
 	bool			use_atu_msg;
 	int			msg_atu_index;
 	struct resource		*msg_res;
+	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 12323b3334a9..68fc8873bc60 100644
--- a/include/uapi/linux/pci_regs.h
+++ b/include/uapi/linux/pci_regs.h
@@ -1118,6 +1118,9 @@
 #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