PCI: qcom: Add equalization settings for 16.0 GT/s

During high data transmission rates such as 16.0 GT/s, there is an
increased risk of signal loss due to poor channel quality and
interference. This can impact receiver's ability to capture signals
accurately.

Hence, as signal compensation is achieved through appropriate lane
equalization, apply lane equalization settings at both transmitter
and receiver which results in an increase in the PCIe signal strength.

While at it, modify the pcie-tegra194 driver to make use of the
common GEN3_EQ_CONTROL_OFF definitions in pcie-designware.h.

Link: https://lore.kernel.org/linux-pci/[email protected]
Tested-by: Johan Hovold <[email protected]>
Signed-off-by: Shashank Babu Chinta Venkata <[email protected]>
[mani: dropped the code refactoring and minor changes]
Signed-off-by: Manivannan Sadhasivam <[email protected]>
[kwilczynski: commit log]
Signed-off-by: Krzysztof Wilczyński <[email protected]>
Reviewed-by: Johan Hovold <[email protected]>
Reviewed-by: Manivannan Sadhasivam <[email protected]>

Author: Shashank Babu Chinta Venkata

MAINTAINERS

@@ -2728,7 +2728,7 @@ F:	drivers/iommu/msm*
 F:	drivers/mfd/ssbi.c
 F:	drivers/mmc/host/mmci_qcom*
 F:	drivers/mmc/host/sdhci-msm.c
-F:	drivers/pci/controller/dwc/pcie-qcom.c
+F:	drivers/pci/controller/dwc/pcie-qcom*
 F:	drivers/phy/qualcomm/
 F:	drivers/power/*/msm*
 F:	drivers/reset/reset-qcom-*
@@ -17754,6 +17754,7 @@ M:	Manivannan Sadhasivam <[email protected]>
 L:	[email protected]
 L:	[email protected]
 S:	Maintained
+F:	drivers/pci/controller/dwc/pcie-qcom-common.c
 F:	drivers/pci/controller/dwc/pcie-qcom.c
 
 PCIE DRIVER FOR ROCKCHIP
@@ -17790,6 +17791,7 @@ L:	[email protected]
 L:	[email protected]
 S:	Maintained
 F:	Documentation/devicetree/bindings/pci/qcom,pcie-ep.yaml
+F:	drivers/pci/controller/dwc/pcie-qcom-common.c
 F:	drivers/pci/controller/dwc/pcie-qcom-ep.c
 
 PCMCIA SUBSYSTEM

drivers/pci/controller/dwc/Kconfig

@@ -265,12 +265,16 @@ config PCIE_DW_PLAT_EP
 	  order to enable device-specific features PCI_DW_PLAT_EP must be
 	  selected.
 
+config PCIE_QCOM_COMMON
+	bool
+
 config PCIE_QCOM
 	bool "Qualcomm PCIe controller (host mode)"
 	depends on OF && (ARCH_QCOM || COMPILE_TEST)
 	depends on PCI_MSI
 	select PCIE_DW_HOST
 	select CRC8
+	select PCIE_QCOM_COMMON
 	help
 	  Say Y here to enable PCIe controller support on Qualcomm SoCs. The
 	  PCIe controller uses the DesignWare core plus Qualcomm-specific
@@ -281,6 +285,7 @@ config PCIE_QCOM_EP
 	depends on OF && (ARCH_QCOM || COMPILE_TEST)
 	depends on PCI_ENDPOINT
 	select PCIE_DW_EP
+	select PCIE_QCOM_COMMON
 	help
 	  Say Y here to enable support for the PCIe controllers on Qualcomm SoCs
 	  to work in endpoint mode. The PCIe controller uses the DesignWare core

drivers/pci/controller/dwc/Makefile

@@ -12,6 +12,7 @@ obj-$(CONFIG_PCIE_SPEAR13XX) += pcie-spear13xx.o
 obj-$(CONFIG_PCI_KEYSTONE) += pci-keystone.o
 obj-$(CONFIG_PCI_LAYERSCAPE) += pci-layerscape.o
 obj-$(CONFIG_PCI_LAYERSCAPE_EP) += pci-layerscape-ep.o
+obj-$(CONFIG_PCIE_QCOM_COMMON) += pcie-qcom-common.o
 obj-$(CONFIG_PCIE_QCOM) += pcie-qcom.o
 obj-$(CONFIG_PCIE_QCOM_EP) += pcie-qcom-ep.o
 obj-$(CONFIG_PCIE_ARMADA_8K) += pcie-armada8k.o

drivers/pci/controller/dwc/pcie-designware.h

@@ -125,6 +125,19 @@
 #define GEN3_RELATED_OFF_GEN3_EQ_DISABLE	BIT(16)
 #define GEN3_RELATED_OFF_RATE_SHADOW_SEL_SHIFT	24
 #define GEN3_RELATED_OFF_RATE_SHADOW_SEL_MASK	GENMASK(25, 24)
+#define GEN3_RELATED_OFF_RATE_SHADOW_SEL_16_0GT	0x1
+
+#define GEN3_EQ_CONTROL_OFF			0x8A8
+#define GEN3_EQ_CONTROL_OFF_FB_MODE		GENMASK(3, 0)
+#define GEN3_EQ_CONTROL_OFF_PHASE23_EXIT_MODE	BIT(4)
+#define GEN3_EQ_CONTROL_OFF_PSET_REQ_VEC	GENMASK(23, 8)
+#define GEN3_EQ_CONTROL_OFF_FOM_INC_INITIAL_EVAL	BIT(24)
+
+#define GEN3_EQ_FB_MODE_DIR_CHANGE_OFF		0x8AC
+#define GEN3_EQ_FMDC_T_MIN_PHASE23		GENMASK(4, 0)
+#define GEN3_EQ_FMDC_N_EVALS			GENMASK(9, 5)
+#define GEN3_EQ_FMDC_MAX_PRE_CUSROR_DELTA	GENMASK(13, 10)
+#define GEN3_EQ_FMDC_MAX_POST_CUSROR_DELTA	GENMASK(17, 14)
 
 #define PCIE_PORT_MULTI_LANE_CTRL	0x8C0
 #define PORT_MLTI_UPCFG_SUPPORT		BIT(7)

drivers/pci/controller/dwc/pcie-qcom-common.c

@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2024 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#include <linux/pci.h>
+
+#include "pcie-designware.h"
+#include "pcie-qcom-common.h"
+
+void qcom_pcie_common_set_16gt_equalization(struct dw_pcie *pci)
+{
+	u32 reg;
+
+	/*
+	 * GEN3_RELATED_OFF register is repurposed to apply equalization
+	 * settings at various data transmission rates through registers namely
+	 * GEN3_EQ_*. The RATE_SHADOW_SEL bit field of GEN3_RELATED_OFF
+	 * determines the data rate for which these equalization settings are
+	 * applied.
+	 */
+	reg = dw_pcie_readl_dbi(pci, GEN3_RELATED_OFF);
+	reg &= ~GEN3_RELATED_OFF_GEN3_ZRXDC_NONCOMPL;
+	reg &= ~GEN3_RELATED_OFF_RATE_SHADOW_SEL_MASK;
+	reg |= FIELD_PREP(GEN3_RELATED_OFF_RATE_SHADOW_SEL_MASK,
+			  GEN3_RELATED_OFF_RATE_SHADOW_SEL_16_0GT);
+	dw_pcie_writel_dbi(pci, GEN3_RELATED_OFF, reg);
+
+	reg = dw_pcie_readl_dbi(pci, GEN3_EQ_FB_MODE_DIR_CHANGE_OFF);
+	reg &= ~(GEN3_EQ_FMDC_T_MIN_PHASE23 |
+		GEN3_EQ_FMDC_N_EVALS |
+		GEN3_EQ_FMDC_MAX_PRE_CUSROR_DELTA |
+		GEN3_EQ_FMDC_MAX_POST_CUSROR_DELTA);
+	reg |= FIELD_PREP(GEN3_EQ_FMDC_T_MIN_PHASE23, 0x1) |
+		FIELD_PREP(GEN3_EQ_FMDC_N_EVALS, 0xd) |
+		FIELD_PREP(GEN3_EQ_FMDC_MAX_PRE_CUSROR_DELTA, 0x5) |
+		FIELD_PREP(GEN3_EQ_FMDC_MAX_POST_CUSROR_DELTA, 0x5);
+	dw_pcie_writel_dbi(pci, GEN3_EQ_FB_MODE_DIR_CHANGE_OFF, reg);
+
+	reg = dw_pcie_readl_dbi(pci, GEN3_EQ_CONTROL_OFF);
+	reg &= ~(GEN3_EQ_CONTROL_OFF_FB_MODE |
+		GEN3_EQ_CONTROL_OFF_PHASE23_EXIT_MODE |
+		GEN3_EQ_CONTROL_OFF_FOM_INC_INITIAL_EVAL |
+		GEN3_EQ_CONTROL_OFF_PSET_REQ_VEC);
+	dw_pcie_writel_dbi(pci, GEN3_EQ_CONTROL_OFF, reg);
+}
+EXPORT_SYMBOL_GPL(qcom_pcie_common_set_16gt_equalization);

drivers/pci/controller/dwc/pcie-qcom-common.h

@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#ifndef _PCIE_QCOM_COMMON_H
+#define _PCIE_QCOM_COMMON_H
+
+struct dw_pcie;
+
+void qcom_pcie_common_set_16gt_equalization(struct dw_pcie *pci);
+
+#endif

drivers/pci/controller/dwc/pcie-qcom-ep.c

@@ -25,6 +25,7 @@
 
 #include "../../pci.h"
 #include "pcie-designware.h"
+#include "pcie-qcom-common.h"
 
 /* PARF registers */
 #define PARF_SYS_CTRL				0x00
@@ -486,6 +487,9 @@ static int qcom_pcie_perst_deassert(struct dw_pcie *pci)
 		goto err_disable_resources;
 	}
 
+	if (pcie_link_speed[pci->max_link_speed] == PCIE_SPEED_16_0GT)
+		qcom_pcie_common_set_16gt_equalization(pci);
+
 	/*
 	 * The physical address of the MMIO region which is exposed as the BAR
 	 * should be written to MHI BASE registers.

drivers/pci/controller/dwc/pcie-qcom.c

@@ -35,6 +35,7 @@
 
 #include "../../pci.h"
 #include "pcie-designware.h"
+#include "pcie-qcom-common.h"
 
 /* PARF registers */
 #define PARF_SYS_CTRL				0x00
@@ -295,6 +296,9 @@ static int qcom_pcie_start_link(struct dw_pcie *pci)
 {
 	struct qcom_pcie *pcie = to_qcom_pcie(pci);
 
+	if (pcie_link_speed[pci->max_link_speed] == PCIE_SPEED_16_0GT)
+		qcom_pcie_common_set_16gt_equalization(pci);
+
 	/* Enable Link Training state machine */
 	if (pcie->cfg->ops->ltssm_enable)
 		pcie->cfg->ops->ltssm_enable(pcie);

drivers/pci/controller/dwc/pcie-tegra194.c

@@ -177,11 +177,6 @@
 #define N_FTS_VAL					52
 #define FTS_VAL						52
 
-#define GEN3_EQ_CONTROL_OFF			0x8a8
-#define GEN3_EQ_CONTROL_OFF_PSET_REQ_VEC_SHIFT	8
-#define GEN3_EQ_CONTROL_OFF_PSET_REQ_VEC_MASK	GENMASK(23, 8)
-#define GEN3_EQ_CONTROL_OFF_FB_MODE_MASK	GENMASK(3, 0)
-
 #define PORT_LOGIC_AMBA_ERROR_RESPONSE_DEFAULT	0x8D0
 #define AMBA_ERROR_RESPONSE_CRS_SHIFT		3
 #define AMBA_ERROR_RESPONSE_CRS_MASK		GENMASK(1, 0)
@@ -861,9 +856,9 @@ static void config_gen3_gen4_eq_presets(struct tegra_pcie_dw *pcie)
 	dw_pcie_writel_dbi(pci, GEN3_RELATED_OFF, val);
 
 	val = dw_pcie_readl_dbi(pci, GEN3_EQ_CONTROL_OFF);
-	val &= ~GEN3_EQ_CONTROL_OFF_PSET_REQ_VEC_MASK;
-	val |= (0x3ff << GEN3_EQ_CONTROL_OFF_PSET_REQ_VEC_SHIFT);
-	val &= ~GEN3_EQ_CONTROL_OFF_FB_MODE_MASK;
+	val &= ~GEN3_EQ_CONTROL_OFF_PSET_REQ_VEC;
+	val |= FIELD_PREP(GEN3_EQ_CONTROL_OFF_PSET_REQ_VEC, 0x3ff);
+	val &= ~GEN3_EQ_CONTROL_OFF_FB_MODE;
 	dw_pcie_writel_dbi(pci, GEN3_EQ_CONTROL_OFF, val);
 
 	val = dw_pcie_readl_dbi(pci, GEN3_RELATED_OFF);
@@ -872,10 +867,10 @@ static void config_gen3_gen4_eq_presets(struct tegra_pcie_dw *pcie)
 	dw_pcie_writel_dbi(pci, GEN3_RELATED_OFF, val);
 
 	val = dw_pcie_readl_dbi(pci, GEN3_EQ_CONTROL_OFF);
-	val &= ~GEN3_EQ_CONTROL_OFF_PSET_REQ_VEC_MASK;
-	val |= (pcie->of_data->gen4_preset_vec <<
-		GEN3_EQ_CONTROL_OFF_PSET_REQ_VEC_SHIFT);
-	val &= ~GEN3_EQ_CONTROL_OFF_FB_MODE_MASK;
+	val &= ~GEN3_EQ_CONTROL_OFF_PSET_REQ_VEC;
+	val |= FIELD_PREP(GEN3_EQ_CONTROL_OFF_PSET_REQ_VEC,
+			  pcie->of_data->gen4_preset_vec);
+	val &= ~GEN3_EQ_CONTROL_OFF_FB_MODE;
 	dw_pcie_writel_dbi(pci, GEN3_EQ_CONTROL_OFF, val);
 
 	val = dw_pcie_readl_dbi(pci, GEN3_RELATED_OFF);