[PATCH v7 0/4] PCI: dwc: Add support for configuring lane equalization presets

[PATCH v7 0/4] 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.

As per PCIe spec 6.0.1 revision section 8.3.3.3 & 4.2.4 for data rates
of 8.0 GT/s, 16.0 GT/s, 32.0 GT/s, and 64.0 GT/s, there is a way to
configure lane equalization presets for each lane to enhance the PCIe
link reliability. Each preset value represents a different combination
of pre-shoot and de-emphasis values. For each data rate, different
registers are defined: for 8.0 GT/s, registers are defined in section
7.7.3.4; for 16.0 GT/s, in section 7.7.5.9, etc. The 8.0 GT/s rate has
an extra receiver preset hint, requiring 16 bits per lane, while the
remaining data rates use 8 bits per lane.

Based on the number of lanes and the supported data rate, read the
device tree property and stores in the presets structure.

Based upon the lane width and supported data rate update lane
equalization registers.

This patch depends on the this dt binding pull request which got recently
merged: https://github.com/devicetree-org/dt-schema/pull/146

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
---
Changes in v7:
- Update the 16bit array in the array (mani & konrad)
- Update the couple of nits (comments, error log format etc) (mani)
- remove !num_lanes check as this is not needed with this series (mani)
- Add warning prints if the data rate is not supported and if there is
  no devicetree property for the data rate (mani).
- Link to v6: https://lore.kernel.org/r/20250210-preset_v6-v6-0-cbd837d0028d@oss.qualcomm.com

Changes in v6:
- update the dt properties to match the lane width ( mani & konard)
- move everything to helper function and let the helper function
  determine reg size and offset (mani)
- update the function header (mani)
- move the num_lanes check to the main function (mani)
- Link to v5: https://lore.kernel.org/linux-kernel/20250128-preset_v2-v5-0-4d230d956f8c@oss.qualcomm.com/

Changes in v5:
- Instead of using of_property_present use return value of
  of_property_read_u8_array to know about property is present or not and
  add a macro for reserved value(Konrad).
- Link to v4: https://lore.kernel.org/r/20250124-preset_v2-v4-0-0b512cad08e1@oss.qualcomm.com

Changes in v4:
- use static arrays for storing preset values and use default value 0xff
  to indicate the property is not present (Dimitry & konrad).
- Link to v3: https://lore.kernel.org/r/20241223-preset_v2-v3-0-a339f475caf5@oss.qualcomm.com

Changes in v3:
- In previous series a wrong patch was attached, correct it
- Link to v2: https://lore.kernel.org/r/20241212-preset_v2-v2-0-210430fbcd8a@oss.qualcomm.com

Changes in v2:
- Fix the kernel test robot error
- As suggested by konrad use for loop and read "eq-presets-%ugts", (8 << i)
- Link to v1: https://lore.kernel.org/r/20241116-presets-v1-0-878a837a4fee@quicinc.com

---
Krishna Chaitanya Chundru (4):
      arm64: dts: qcom: x1e80100: Add PCIe lane equalization preset properties
      PCI: of: Add API to retrieve equalization presets from device tree
      PCI: dwc: Improve handling of PCIe lane configuration
      PCI: dwc: Add support for configuring lane equalization presets

 arch/arm64/boot/dts/qcom/x1e80100.dtsi            | 13 +++++
 drivers/pci/controller/dwc/pcie-designware-host.c | 69 +++++++++++++++++++++++
 drivers/pci/controller/dwc/pcie-designware.c      | 11 +++-
 drivers/pci/controller/dwc/pcie-designware.h      |  4 ++
 drivers/pci/of.c                                  | 43 ++++++++++++++
 drivers/pci/pci.h                                 | 27 ++++++++-
 include/uapi/linux/pci_regs.h                     |  3 +
 7 files changed, 168 insertions(+), 2 deletions(-)
---
base-commit: 3175967ecb3266d0ad7d2ca7ccceaf15fa2f15e2
change-id: 20250210-preset_v6-1e7f560d13ad

Best regards,
-- 
Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>

[PATCH v7 1/4] arm64: dts: qcom: x1e80100: Add PCIe lane equalization preset properties

[Krishna Chaitanya Chundru]

Add PCIe lane equalization preset properties for 8 GT/s and 16 GT/s data
rates used in lane equalization procedure.

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
---
This patch depends on the this dt binding pull request which got recently
merged: https://github.com/devicetree-org/dt-schema/pull/146
---
---
 arch/arm64/boot/dts/qcom/x1e80100.dtsi | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/arm64/boot/dts/qcom/x1e80100.dtsi b/arch/arm64/boot/dts/qcom/x1e80100.dtsi
index 4936fa5b98ff..9a18b8f90145 100644
--- a/arch/arm64/boot/dts/qcom/x1e80100.dtsi
+++ b/arch/arm64/boot/dts/qcom/x1e80100.dtsi
@@ -3209,6 +3209,11 @@ &mc_virt SLAVE_EBI1 QCOM_ICC_TAG_ALWAYS>,
 			phys = <&pcie3_phy>;
 			phy-names = "pciephy";
 
+			eq-presets-8gts = /bits/ 16 <0x5555 0x5555 0x5555 0x5555
+						     0x5555 0x5555 0x5555 0x5555>;
+
+			eq-presets-16gts = /bits/ 8 <0x55 0x55 0x55 0x55 0x55 0x55 0x55 0x55>;
+
 			operating-points-v2 = <&pcie3_opp_table>;
 
 			status = "disabled";
@@ -3411,6 +3416,10 @@ &mc_virt SLAVE_EBI1 QCOM_ICC_TAG_ALWAYS>,
 			phys = <&pcie6a_phy>;
 			phy-names = "pciephy";
 
+			eq-presets-8gts = /bits/ 16 <0x5555 0x5555 0x5555 0x5555>;
+
+			eq-presets-16gts = /bits/ 8 <0x55 0x55 0x55 0x55>;
+
 			status = "disabled";
 		};
 
@@ -3538,6 +3547,8 @@ &mc_virt SLAVE_EBI1 QCOM_ICC_TAG_ALWAYS>,
 			phys = <&pcie5_phy>;
 			phy-names = "pciephy";
 
+			eq-presets-8gts = /bits/ 16 <0x5555 0x5555>;
+
 			status = "disabled";
 		};
 
@@ -3662,6 +3673,8 @@ &mc_virt SLAVE_EBI1 QCOM_ICC_TAG_ALWAYS>,
 			phys = <&pcie4_phy>;
 			phy-names = "pciephy";
 
+			eq-presets-8gts = /bits/ 16 <0x5555 0x5555>;
+
 			status = "disabled";
 
 			pcie4_port0: pcie@0 {

-- 
2.34.1

[PATCH v7 2/4] PCI: of: Add API to retrieve equalization presets from device tree

[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.

As per PCIe spec 6.0.1 revision section 8.3.3.3 & 4.2.4 for data rates
of 8.0 GT/s, 16.0 GT/s, 32.0 GT/s, and 64.0 GT/s, there is a way to
configure lane equalization presets for each lane to enhance the PCIe
link reliability. Each preset value represents a different combination
of pre-shoot and de-emphasis values. For each data rate, different
registers are defined: for 8.0 GT/s, registers are defined in section
7.7.3.4; for 16.0 GT/s, in section 7.7.5.9, etc. The 8.0 GT/s rate has
an extra receiver preset hint, requiring 16 bits per lane, while the
remaining data rates use 8 bits per lane.

Based on the number of lanes and the supported data rate, this function
reads the device tree property and stores in the presets structure.

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
---
 drivers/pci/of.c  | 43 +++++++++++++++++++++++++++++++++++++++++++
 drivers/pci/pci.h | 27 ++++++++++++++++++++++++++-
 2 files changed, 69 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index 7a806f5c0d20..9ebe7d0e4e0c 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -851,3 +851,46 @@ u32 of_pci_get_slot_power_limit(struct device_node *node,
 	return slot_power_limit_mw;
 }
 EXPORT_SYMBOL_GPL(of_pci_get_slot_power_limit);
+
+/**
+ * of_pci_get_equalization_presets - Parses the "eq-presets-Ngts" property.
+ *
+ * @dev: Device containing the properties.
+ * @presets: Pointer to store the parsed data.
+ * @num_lanes: Maximum number of lanes supported.
+ *
+ * If the property is present read and store the data in the preset structure
+ * else assign default value 0xff to indicate property is not present.
+ *
+ * Return: 0 if the property is not available or successfully parsed; errno otherwise.
+ */
+int of_pci_get_equalization_presets(struct device *dev,
+				    struct pci_eq_presets *presets,
+				    int num_lanes)
+{
+	char name[20];
+	int ret;
+
+	presets->eq_presets_8gts[0] = PCI_EQ_RESV;
+	ret = of_property_read_u16_array(dev->of_node, "eq-presets-8gts",
+					 presets->eq_presets_8gts, num_lanes);
+	if (ret && ret != -EINVAL) {
+		dev_err(dev, "Error reading eq-presets-8gts :%d\n", ret);
+		return ret;
+	}
+
+	for (int i = 0; i < EQ_PRESET_TYPE_MAX; i++) {
+		presets->eq_presets_Ngts[i][0] = PCI_EQ_RESV;
+		snprintf(name, sizeof(name), "eq-presets-%dgts", 8 << (i + 1));
+		ret = of_property_read_u8_array(dev->of_node, name,
+						presets->eq_presets_Ngts[i],
+						num_lanes);
+		if (ret && ret != -EINVAL) {
+			dev_err(dev, "Error reading %s :%d\n", name, ret);
+			return ret;
+		}
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(of_pci_get_equalization_presets);
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 01e51db8d285..c8d44b21ef03 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -9,6 +9,8 @@ struct pcie_tlp_log;
 /* Number of possible devfns: 0.0 to 1f.7 inclusive */
 #define MAX_NR_DEVFNS 256
 
+#define MAX_NR_LANES 16
+
 #define PCI_FIND_CAP_TTL	48
 
 #define PCI_VSEC_ID_INTEL_TBT	0x1234	/* Thunderbolt */
@@ -808,6 +810,20 @@ static inline u64 pci_rebar_size_to_bytes(int size)
 
 struct device_node;
 
+#define PCI_EQ_RESV	0xff
+
+enum equalization_preset_type {
+	EQ_PRESET_TYPE_16GTS,
+	EQ_PRESET_TYPE_32GTS,
+	EQ_PRESET_TYPE_64GTS,
+	EQ_PRESET_TYPE_MAX
+};
+
+struct pci_eq_presets {
+	u16 eq_presets_8gts[MAX_NR_LANES];
+	u8 eq_presets_Ngts[EQ_PRESET_TYPE_MAX][MAX_NR_LANES];
+};
+
 #ifdef CONFIG_OF
 int of_get_pci_domain_nr(struct device_node *node);
 int of_pci_get_max_link_speed(struct device_node *node);
@@ -822,7 +838,9 @@ void pci_release_bus_of_node(struct pci_bus *bus);
 
 int devm_of_pci_bridge_init(struct device *dev, struct pci_host_bridge *bridge);
 bool of_pci_supply_present(struct device_node *np);
-
+int of_pci_get_equalization_presets(struct device *dev,
+				    struct pci_eq_presets *presets,
+				    int num_lanes);
 #else
 static inline int
 of_get_pci_domain_nr(struct device_node *node)
@@ -867,6 +885,13 @@ static inline bool of_pci_supply_present(struct device_node *np)
 {
 	return false;
 }
+
+static inline int of_pci_get_equalization_presets(struct device *dev,
+						  struct pci_eq_presets *presets,
+						  int num_lanes)
+{
+	return 0;
+}
 #endif /* CONFIG_OF */
 
 struct of_changeset;

-- 
2.34.1

[PATCH v7 3/4] PCI: dwc: Improve handling of PCIe lane configuration

[Krishna Chaitanya Chundru]

Currently even if the number of lanes hardware supports is equal to
the number lanes provided in the devicetree, the driver is trying to
configure again the maximum number of lanes which is not needed.

Update number of lanes only when it is not equal to hardware capability.

And also if the num-lanes property is not present in the devicetree
update the num_lanes with the maximum hardware supports.

Introduce dw_pcie_link_get_max_link_width() to get the maximum lane
width the hardware supports.

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
---
 drivers/pci/controller/dwc/pcie-designware-host.c |  3 +++
 drivers/pci/controller/dwc/pcie-designware.c      | 11 ++++++++++-
 drivers/pci/controller/dwc/pcie-designware.h      |  1 +
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index ffaded8f2df7..dd56cc02f4ef 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c
@@ -504,6 +504,9 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
 
 	dw_pcie_iatu_detect(pci);
 
+	if (pci->num_lanes < 1)
+		pci->num_lanes = dw_pcie_link_get_max_link_width(pci);
+
 	/*
 	 * Allocate the resource for MSG TLP before programming the iATU
 	 * outbound window in dw_pcie_setup_rc(). Since the allocation depends
diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
index 145e7f579072..9fc5916867b6 100644
--- a/drivers/pci/controller/dwc/pcie-designware.c
+++ b/drivers/pci/controller/dwc/pcie-designware.c
@@ -737,12 +737,21 @@ static void dw_pcie_link_set_max_speed(struct dw_pcie *pci)
 
 }
 
+int dw_pcie_link_get_max_link_width(struct dw_pcie *pci)
+{
+	u8 cap = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
+	u32 lnkcap = dw_pcie_readl_dbi(pci, cap + PCI_EXP_LNKCAP);
+
+	return FIELD_GET(PCI_EXP_LNKCAP_MLW, lnkcap);
+}
+
 static void dw_pcie_link_set_max_link_width(struct dw_pcie *pci, u32 num_lanes)
 {
+	int max_lanes = dw_pcie_link_get_max_link_width(pci);
 	u32 lnkcap, lwsc, plc;
 	u8 cap;
 
-	if (!num_lanes)
+	if (max_lanes == num_lanes)
 		return;
 
 	/* Set the number of lanes */
diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
index 501d9ddfea16..61d1fb6b437b 100644
--- a/drivers/pci/controller/dwc/pcie-designware.h
+++ b/drivers/pci/controller/dwc/pcie-designware.h
@@ -488,6 +488,7 @@ void dw_pcie_write_dbi2(struct dw_pcie *pci, u32 reg, size_t size, u32 val);
 int dw_pcie_link_up(struct dw_pcie *pci);
 void dw_pcie_upconfig_setup(struct dw_pcie *pci);
 int dw_pcie_wait_for_link(struct dw_pcie *pci);
+int dw_pcie_link_get_max_link_width(struct dw_pcie *pci);
 int dw_pcie_prog_outbound_atu(struct dw_pcie *pci,
 			      const struct dw_pcie_ob_atu_cfg *atu);
 int dw_pcie_prog_inbound_atu(struct dw_pcie *pci, int index, int type,

-- 
2.34.1

[PATCH v7 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, 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

Re: [PATCH v7 2/4] PCI: of: Add API to retrieve equalization presets from device tree

[Bjorn Helgaas]

On Tue, Feb 25, 2025 at 05:15:05PM +0530, Krishna Chaitanya Chundru wrote:
> PCIe equalization presets are predefined settings used to optimize
> signal integrity by compensating for signal loss and distortion in
> high-speed data transmission.
> 
> As per PCIe spec 6.0.1 revision section 8.3.3.3 & 4.2.4 for data rates
> of 8.0 GT/s, 16.0 GT/s, 32.0 GT/s, and 64.0 GT/s, there is a way to
> configure lane equalization presets for each lane to enhance the PCIe
> link reliability. Each preset value represents a different combination
> of pre-shoot and de-emphasis values. For each data rate, different
> registers are defined: for 8.0 GT/s, registers are defined in section
> 7.7.3.4; for 16.0 GT/s, in section 7.7.5.9, etc. The 8.0 GT/s rate has
> an extra receiver preset hint, requiring 16 bits per lane, while the
> remaining data rates use 8 bits per lane.
> 
> Based on the number of lanes and the supported data rate, this function
> reads the device tree property and stores in the presets structure.

Can you mention the function name here somewhere so we don't have to
dig it out of the patch?  If you put it in the subject, the function
name is descriptive enough that you hardly need anything more, e.g.,

  PCI: of: Add of_pci_get_equalization_presets() API

> + * of_pci_get_equalization_presets - Parses the "eq-presets-Ngts" property.
> + *
> + * @dev: Device containing the properties.
> + * @presets: Pointer to store the parsed data.
> + * @num_lanes: Maximum number of lanes supported.
> + *
> + * If the property is present read and store the data in the preset structure
> + * else assign default value 0xff to indicate property is not present.
> + *
> + * Return: 0 if the property is not available or successfully parsed; errno otherwise.

Wrap to fit in 80 columns like the rest of the file.

> + */
> +int of_pci_get_equalization_presets(struct device *dev,
> +				    struct pci_eq_presets *presets,
> +				    int num_lanes)
> +{

Re: [PATCH v7 1/4] arm64: dts: qcom: x1e80100: Add PCIe lane equalization preset properties

[Manivannan Sadhasivam]

On Tue, Feb 25, 2025 at 05:15:04PM +0530, Krishna Chaitanya Chundru wrote:
> Add PCIe lane equalization preset properties for 8 GT/s and 16 GT/s data
> rates used in lane equalization procedure.
> 
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

One minor nit below.

> Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
> ---
> This patch depends on the this dt binding pull request which got recently
> merged: https://github.com/devicetree-org/dt-schema/pull/146
> ---
> ---
>  arch/arm64/boot/dts/qcom/x1e80100.dtsi | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/qcom/x1e80100.dtsi b/arch/arm64/boot/dts/qcom/x1e80100.dtsi
> index 4936fa5b98ff..9a18b8f90145 100644
> --- a/arch/arm64/boot/dts/qcom/x1e80100.dtsi
> +++ b/arch/arm64/boot/dts/qcom/x1e80100.dtsi
> @@ -3209,6 +3209,11 @@ &mc_virt SLAVE_EBI1 QCOM_ICC_TAG_ALWAYS>,
>  			phys = <&pcie3_phy>;
>  			phy-names = "pciephy";
>  
> +			eq-presets-8gts = /bits/ 16 <0x5555 0x5555 0x5555 0x5555
> +						     0x5555 0x5555 0x5555 0x5555>;
> +

Get rid of the newline between eq-presets-8gts and eq-presets-16gts.

- Mani

-- 
மணிவண்ணன் சதாசிவம்

Re: [PATCH v7 2/4] PCI: of: Add API to retrieve equalization presets from device tree

[Manivannan Sadhasivam]

On Tue, Feb 25, 2025 at 05:15:05PM +0530, Krishna Chaitanya Chundru wrote:
> PCIe equalization presets are predefined settings used to optimize
> signal integrity by compensating for signal loss and distortion in
> high-speed data transmission.
> 
> As per PCIe spec 6.0.1 revision section 8.3.3.3 & 4.2.4 for data rates
> of 8.0 GT/s, 16.0 GT/s, 32.0 GT/s, and 64.0 GT/s, there is a way to
> configure lane equalization presets for each lane to enhance the PCIe
> link reliability. Each preset value represents a different combination
> of pre-shoot and de-emphasis values. For each data rate, different
> registers are defined: for 8.0 GT/s, registers are defined in section
> 7.7.3.4; for 16.0 GT/s, in section 7.7.5.9, etc. The 8.0 GT/s rate has
> an extra receiver preset hint, requiring 16 bits per lane, while the
> remaining data rates use 8 bits per lane.
> 
> Based on the number of lanes and the supported data rate, this function
> reads the device tree property and stores in the presets structure.
> 
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
> ---
>  drivers/pci/of.c  | 43 +++++++++++++++++++++++++++++++++++++++++++
>  drivers/pci/pci.h | 27 ++++++++++++++++++++++++++-
>  2 files changed, 69 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> index 7a806f5c0d20..9ebe7d0e4e0c 100644
> --- a/drivers/pci/of.c
> +++ b/drivers/pci/of.c
> @@ -851,3 +851,46 @@ u32 of_pci_get_slot_power_limit(struct device_node *node,
>  	return slot_power_limit_mw;
>  }
>  EXPORT_SYMBOL_GPL(of_pci_get_slot_power_limit);
> +
> +/**
> + * of_pci_get_equalization_presets - Parses the "eq-presets-Ngts" property.
> + *
> + * @dev: Device containing the properties.
> + * @presets: Pointer to store the parsed data.
> + * @num_lanes: Maximum number of lanes supported.
> + *
> + * If the property is present read and store the data in the preset structure
> + * else assign default value 0xff to indicate property is not present.

'If the property is present, read and store the data in the @presets structure.
Else, assign a default value of PCI_EQ_RESV.'

> + *
> + * Return: 0 if the property is not available or successfully parsed; errno otherwise.
> + */
> +int of_pci_get_equalization_presets(struct device *dev,
> +				    struct pci_eq_presets *presets,
> +				    int num_lanes)
> +{
> +	char name[20];
> +	int ret;
> +
> +	presets->eq_presets_8gts[0] = PCI_EQ_RESV;
> +	ret = of_property_read_u16_array(dev->of_node, "eq-presets-8gts",
> +					 presets->eq_presets_8gts, num_lanes);
> +	if (ret && ret != -EINVAL) {
> +		dev_err(dev, "Error reading eq-presets-8gts :%d\n", ret);
> +		return ret;
> +	}
> +
> +	for (int i = 0; i < EQ_PRESET_TYPE_MAX; i++) {
> +		presets->eq_presets_Ngts[i][0] = PCI_EQ_RESV;
> +		snprintf(name, sizeof(name), "eq-presets-%dgts", 8 << (i + 1));
> +		ret = of_property_read_u8_array(dev->of_node, name,
> +						presets->eq_presets_Ngts[i],
> +						num_lanes);
> +		if (ret && ret != -EINVAL) {
> +			dev_err(dev, "Error reading %s :%d\n", name, ret);
> +			return ret;
> +		}
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(of_pci_get_equalization_presets);
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 01e51db8d285..c8d44b21ef03 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -9,6 +9,8 @@ struct pcie_tlp_log;
>  /* Number of possible devfns: 0.0 to 1f.7 inclusive */
>  #define MAX_NR_DEVFNS 256
>  
> +#define MAX_NR_LANES 16
> +
>  #define PCI_FIND_CAP_TTL	48
>  
>  #define PCI_VSEC_ID_INTEL_TBT	0x1234	/* Thunderbolt */
> @@ -808,6 +810,20 @@ static inline u64 pci_rebar_size_to_bytes(int size)
>  
>  struct device_node;
>  
> +#define PCI_EQ_RESV	0xff
> +
> +enum equalization_preset_type {

For the sake of completeness, you should add EQ_PRESET_TYPE_8GTS also. You could
skip it while reading the of_property_read_u8_array().

> +	EQ_PRESET_TYPE_16GTS,
> +	EQ_PRESET_TYPE_32GTS,
> +	EQ_PRESET_TYPE_64GTS,
> +	EQ_PRESET_TYPE_MAX
> +};
> +
> +struct pci_eq_presets {
> +	u16 eq_presets_8gts[MAX_NR_LANES];
> +	u8 eq_presets_Ngts[EQ_PRESET_TYPE_MAX][MAX_NR_LANES];
> +};
> +
>  #ifdef CONFIG_OF
>  int of_get_pci_domain_nr(struct device_node *node);
>  int of_pci_get_max_link_speed(struct device_node *node);
> @@ -822,7 +838,9 @@ void pci_release_bus_of_node(struct pci_bus *bus);
>  
>  int devm_of_pci_bridge_init(struct device *dev, struct pci_host_bridge *bridge);
>  bool of_pci_supply_present(struct device_node *np);
> -
> +int of_pci_get_equalization_presets(struct device *dev,
> +				    struct pci_eq_presets *presets,
> +				    int num_lanes);
>  #else
>  static inline int
>  of_get_pci_domain_nr(struct device_node *node)
> @@ -867,6 +885,13 @@ static inline bool of_pci_supply_present(struct device_node *np)
>  {
>  	return false;
>  }
> +
> +static inline int of_pci_get_equalization_presets(struct device *dev,
> +						  struct pci_eq_presets *presets,
> +						  int num_lanes)
> +{

Don't you need to initialize presets to PCI_EQ_RESV?

- Mani

-- 
மணிவண்ணன் சதாசிவம்

Re: [PATCH v7 3/4] PCI: dwc: Improve handling of PCIe lane configuration

[Manivannan Sadhasivam]

On Tue, Feb 25, 2025 at 05:15:06PM +0530, Krishna Chaitanya Chundru wrote:
> Currently even if the number of lanes hardware supports is equal to
> the number lanes provided in the devicetree, the driver is trying to
> configure again the maximum number of lanes which is not needed.
> 
> Update number of lanes only when it is not equal to hardware capability.
> 

'Update max link width only...'

> And also if the num-lanes property is not present in the devicetree
> update the num_lanes with the maximum hardware supports.

'...update 'pci->num_lanes' with the hardware supported maximum link width using
the newly introduced dw_pcie_link_get_max_link_width() API.'

> 
> Introduce dw_pcie_link_get_max_link_width() to get the maximum lane
> width the hardware supports.
> 
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
> ---
>  drivers/pci/controller/dwc/pcie-designware-host.c |  3 +++
>  drivers/pci/controller/dwc/pcie-designware.c      | 11 ++++++++++-
>  drivers/pci/controller/dwc/pcie-designware.h      |  1 +
>  3 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index ffaded8f2df7..dd56cc02f4ef 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -504,6 +504,9 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
>  
>  	dw_pcie_iatu_detect(pci);
>  
> +	if (pci->num_lanes < 1)
> +		pci->num_lanes = dw_pcie_link_get_max_link_width(pci);
> +
>  	/*
>  	 * Allocate the resource for MSG TLP before programming the iATU
>  	 * outbound window in dw_pcie_setup_rc(). Since the allocation depends
> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> index 145e7f579072..9fc5916867b6 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.c
> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> @@ -737,12 +737,21 @@ static void dw_pcie_link_set_max_speed(struct dw_pcie *pci)
>  
>  }
>  
> +int dw_pcie_link_get_max_link_width(struct dw_pcie *pci)
> +{
> +	u8 cap = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> +	u32 lnkcap = dw_pcie_readl_dbi(pci, cap + PCI_EXP_LNKCAP);
> +
> +	return FIELD_GET(PCI_EXP_LNKCAP_MLW, lnkcap);
> +}
> +
>  static void dw_pcie_link_set_max_link_width(struct dw_pcie *pci, u32 num_lanes)
>  {
> +	int max_lanes = dw_pcie_link_get_max_link_width(pci);
>  	u32 lnkcap, lwsc, plc;
>  	u8 cap;
>  
> -	if (!num_lanes)
> +	if (max_lanes == num_lanes)

This gives the assumption that the link width in PCIE_PORT_LINK_CONTROL and
PCIE_LINK_WIDTH_SPEED_CONTROL registers are same as MLW. Is it really true as
per the DWC spec?

- Mani

-- 
மணிவண்ணன் சதாசிவம்

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

[Manivannan Sadhasivam]

On Tue, Feb 25, 2025 at 05:15:07PM +0530, Krishna Chaitanya Chundru wrote:
> 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));

No, this is not what I asked for. You should warn only when there is atleast one
of the preset properties are specified in DT. But I think that would complicate
the code. So let's just trust DT here and add the warning later if needed.

> +		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));

Same here. This is going to trigger warning on all DWC platforms. Please remove
it.

- Mani

-- 
மணிவண்ணன் சதாசிவம்

Re: [PATCH v7 2/4] PCI: of: Add API to retrieve equalization presets from device tree

[Krishna Chaitanya Chundru]

On 3/6/2025 8:52 AM, Manivannan Sadhasivam wrote:
> On Tue, Feb 25, 2025 at 05:15:05PM +0530, Krishna Chaitanya Chundru wrote:
>> PCIe equalization presets are predefined settings used to optimize
>> signal integrity by compensating for signal loss and distortion in
>> high-speed data transmission.
>>
>> As per PCIe spec 6.0.1 revision section 8.3.3.3 & 4.2.4 for data rates
>> of 8.0 GT/s, 16.0 GT/s, 32.0 GT/s, and 64.0 GT/s, there is a way to
>> configure lane equalization presets for each lane to enhance the PCIe
>> link reliability. Each preset value represents a different combination
>> of pre-shoot and de-emphasis values. For each data rate, different
>> registers are defined: for 8.0 GT/s, registers are defined in section
>> 7.7.3.4; for 16.0 GT/s, in section 7.7.5.9, etc. The 8.0 GT/s rate has
>> an extra receiver preset hint, requiring 16 bits per lane, while the
>> remaining data rates use 8 bits per lane.
>>
>> Based on the number of lanes and the supported data rate, this function
>> reads the device tree property and stores in the presets structure.
>>
>> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
>> ---
>>   drivers/pci/of.c  | 43 +++++++++++++++++++++++++++++++++++++++++++
>>   drivers/pci/pci.h | 27 ++++++++++++++++++++++++++-
>>   2 files changed, 69 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
>> index 7a806f5c0d20..9ebe7d0e4e0c 100644
>> --- a/drivers/pci/of.c
>> +++ b/drivers/pci/of.c
>> @@ -851,3 +851,46 @@ u32 of_pci_get_slot_power_limit(struct device_node *node,
>>   	return slot_power_limit_mw;
>>   }
>>   EXPORT_SYMBOL_GPL(of_pci_get_slot_power_limit);
>> +
>> +/**
>> + * of_pci_get_equalization_presets - Parses the "eq-presets-Ngts" property.
>> + *
>> + * @dev: Device containing the properties.
>> + * @presets: Pointer to store the parsed data.
>> + * @num_lanes: Maximum number of lanes supported.
>> + *
>> + * If the property is present read and store the data in the preset structure
>> + * else assign default value 0xff to indicate property is not present.
> 
> 'If the property is present, read and store the data in the @presets structure.
> Else, assign a default value of PCI_EQ_RESV.'
> 
>> + *
>> + * Return: 0 if the property is not available or successfully parsed; errno otherwise.
>> + */
>> +int of_pci_get_equalization_presets(struct device *dev,
>> +				    struct pci_eq_presets *presets,
>> +				    int num_lanes)
>> +{
>> +	char name[20];
>> +	int ret;
>> +
>> +	presets->eq_presets_8gts[0] = PCI_EQ_RESV;
>> +	ret = of_property_read_u16_array(dev->of_node, "eq-presets-8gts",
>> +					 presets->eq_presets_8gts, num_lanes);
>> +	if (ret && ret != -EINVAL) {
>> +		dev_err(dev, "Error reading eq-presets-8gts :%d\n", ret);
>> +		return ret;
>> +	}
>> +
>> +	for (int i = 0; i < EQ_PRESET_TYPE_MAX; i++) {
>> +		presets->eq_presets_Ngts[i][0] = PCI_EQ_RESV;
>> +		snprintf(name, sizeof(name), "eq-presets-%dgts", 8 << (i + 1));
>> +		ret = of_property_read_u8_array(dev->of_node, name,
>> +						presets->eq_presets_Ngts[i],
>> +						num_lanes);
>> +		if (ret && ret != -EINVAL) {
>> +			dev_err(dev, "Error reading %s :%d\n", name, ret);
>> +			return ret;
>> +		}
>> +	}
>> +
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(of_pci_get_equalization_presets);
>> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
>> index 01e51db8d285..c8d44b21ef03 100644
>> --- a/drivers/pci/pci.h
>> +++ b/drivers/pci/pci.h
>> @@ -9,6 +9,8 @@ struct pcie_tlp_log;
>>   /* Number of possible devfns: 0.0 to 1f.7 inclusive */
>>   #define MAX_NR_DEVFNS 256
>>   
>> +#define MAX_NR_LANES 16
>> +
>>   #define PCI_FIND_CAP_TTL	48
>>   
>>   #define PCI_VSEC_ID_INTEL_TBT	0x1234	/* Thunderbolt */
>> @@ -808,6 +810,20 @@ static inline u64 pci_rebar_size_to_bytes(int size)
>>   
>>   struct device_node;
>>   
>> +#define PCI_EQ_RESV	0xff
>> +
>> +enum equalization_preset_type {
> 
> For the sake of completeness, you should add EQ_PRESET_TYPE_8GTS also. You could
> skip it while reading the of_property_read_u8_array().
Can we add like this to make parsing logic easier otherwise while
deference the presets array we need to subtract -1.
currently we are using like this presets[EQ_PRESET_TYPE_16GTS] if
we want to keep in same way we need to use like below.

	EQ_PRESET_TYPE_8GTS,
	EQ_PRESET_TYPE_16GTS = 0,
> 
>> +	EQ_PRESET_TYPE_16GTS,
>> +	EQ_PRESET_TYPE_32GTS,
>> +	EQ_PRESET_TYPE_64GTS,
>> +	EQ_PRESET_TYPE_MAX
>> +};
>> +
>> +struct pci_eq_presets {
>> +	u16 eq_presets_8gts[MAX_NR_LANES];
>> +	u8 eq_presets_Ngts[EQ_PRESET_TYPE_MAX][MAX_NR_LANES];
>> +};
>> +
>>   #ifdef CONFIG_OF
>>   int of_get_pci_domain_nr(struct device_node *node);
>>   int of_pci_get_max_link_speed(struct device_node *node);
>> @@ -822,7 +838,9 @@ void pci_release_bus_of_node(struct pci_bus *bus);
>>   
>>   int devm_of_pci_bridge_init(struct device *dev, struct pci_host_bridge *bridge);
>>   bool of_pci_supply_present(struct device_node *np);
>> -
>> +int of_pci_get_equalization_presets(struct device *dev,
>> +				    struct pci_eq_presets *presets,
>> +				    int num_lanes);
>>   #else
>>   static inline int
>>   of_get_pci_domain_nr(struct device_node *node)
>> @@ -867,6 +885,13 @@ static inline bool of_pci_supply_present(struct device_node *np)
>>   {
>>   	return false;
>>   }
>> +
>> +static inline int of_pci_get_equalization_presets(struct device *dev,
>> +						  struct pci_eq_presets *presets,
>> +						  int num_lanes)
>> +{
> 
> Don't you need to initialize presets to PCI_EQ_RESV?
> 
I will update in the next patch.

- Krishna Chaitanya.
> - Mani
> 

Re: [PATCH v7 3/4] PCI: dwc: Improve handling of PCIe lane configuration

[Krishna Chaitanya Chundru]

On 3/6/2025 9:14 AM, Manivannan Sadhasivam wrote:
> On Tue, Feb 25, 2025 at 05:15:06PM +0530, Krishna Chaitanya Chundru wrote:
>> Currently even if the number of lanes hardware supports is equal to
>> the number lanes provided in the devicetree, the driver is trying to
>> configure again the maximum number of lanes which is not needed.
>>
>> Update number of lanes only when it is not equal to hardware capability.
>>
> 
> 'Update max link width only...'
> 
>> And also if the num-lanes property is not present in the devicetree
>> update the num_lanes with the maximum hardware supports.
> 
> '...update 'pci->num_lanes' with the hardware supported maximum link width using
> the newly introduced dw_pcie_link_get_max_link_width() API.'
> 
>>
>> Introduce dw_pcie_link_get_max_link_width() to get the maximum lane
>> width the hardware supports.
>>
>> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
>> ---
>>   drivers/pci/controller/dwc/pcie-designware-host.c |  3 +++
>>   drivers/pci/controller/dwc/pcie-designware.c      | 11 ++++++++++-
>>   drivers/pci/controller/dwc/pcie-designware.h      |  1 +
>>   3 files changed, 14 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
>> index ffaded8f2df7..dd56cc02f4ef 100644
>> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
>> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
>> @@ -504,6 +504,9 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
>>   
>>   	dw_pcie_iatu_detect(pci);
>>   
>> +	if (pci->num_lanes < 1)
>> +		pci->num_lanes = dw_pcie_link_get_max_link_width(pci);
>> +
>>   	/*
>>   	 * Allocate the resource for MSG TLP before programming the iATU
>>   	 * outbound window in dw_pcie_setup_rc(). Since the allocation depends
>> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
>> index 145e7f579072..9fc5916867b6 100644
>> --- a/drivers/pci/controller/dwc/pcie-designware.c
>> +++ b/drivers/pci/controller/dwc/pcie-designware.c
>> @@ -737,12 +737,21 @@ static void dw_pcie_link_set_max_speed(struct dw_pcie *pci)
>>   
>>   }
>>   
>> +int dw_pcie_link_get_max_link_width(struct dw_pcie *pci)
>> +{
>> +	u8 cap = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
>> +	u32 lnkcap = dw_pcie_readl_dbi(pci, cap + PCI_EXP_LNKCAP);
>> +
>> +	return FIELD_GET(PCI_EXP_LNKCAP_MLW, lnkcap);
>> +}
>> +
>>   static void dw_pcie_link_set_max_link_width(struct dw_pcie *pci, u32 num_lanes)
>>   {
>> +	int max_lanes = dw_pcie_link_get_max_link_width(pci);
>>   	u32 lnkcap, lwsc, plc;
>>   	u8 cap;
>>   
>> -	if (!num_lanes)
>> +	if (max_lanes == num_lanes)
> 
> This gives the assumption that the link width in PCIE_PORT_LINK_CONTROL and
> PCIE_LINK_WIDTH_SPEED_CONTROL registers are same as MLW. Is it really true as
> per the DWC spec?
> 
You are correct both the values are not matching and as we are not sure
side effect of not updating it I will revert this logic.

- Krishna Chaitanya.
> - Mani
> 

Re: [PATCH v7 2/4] PCI: of: Add API to retrieve equalization presets from device tree

[Manivannan Sadhasivam]

On Tue, Mar 11, 2025 at 04:31:33PM +0530, Krishna Chaitanya Chundru wrote:

[...]

> > > diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> > > index 01e51db8d285..c8d44b21ef03 100644
> > > --- a/drivers/pci/pci.h
> > > +++ b/drivers/pci/pci.h
> > > @@ -9,6 +9,8 @@ struct pcie_tlp_log;
> > >   /* Number of possible devfns: 0.0 to 1f.7 inclusive */
> > >   #define MAX_NR_DEVFNS 256
> > > +#define MAX_NR_LANES 16
> > > +
> > >   #define PCI_FIND_CAP_TTL	48
> > >   #define PCI_VSEC_ID_INTEL_TBT	0x1234	/* Thunderbolt */
> > > @@ -808,6 +810,20 @@ static inline u64 pci_rebar_size_to_bytes(int size)
> > >   struct device_node;
> > > +#define PCI_EQ_RESV	0xff
> > > +
> > > +enum equalization_preset_type {
> > 
> > For the sake of completeness, you should add EQ_PRESET_TYPE_8GTS also. You could
> > skip it while reading the of_property_read_u8_array().
> Can we add like this to make parsing logic easier otherwise while
> deference the presets array we need to subtract -1.

Without EQ_PRESET_TYPE_8GTS, it would look like a missing enum. So someone will
add EQ_PRESET_TYPE_8GTS in the future and it will break the driver. So be
prepared for it. 

> currently we are using like this presets[EQ_PRESET_TYPE_16GTS] if
> we want to keep in same way we need to use like below.
> 
> 	EQ_PRESET_TYPE_8GTS,
> 	EQ_PRESET_TYPE_16GTS = 0,

No. First enum element should be initialized with 0.

- Mani

-- 
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