Commit 57a4591d authored by Krishna Chaitanya Chundru's avatar Krishna Chaitanya Chundru Committed by Manivannan Sadhasivam
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PCI: of: Add of_pci_get_equalization_presets() API 



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,
of_pci_get_equalization_presets() reads the device tree property and
stores in the presets structure.

Signed-off-by: default avatarKrishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
Signed-off-by: default avatarManivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: default avatarManivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://patch.msgid.link/20250328-preset_v6-v9-2-22cfa0490518@oss.qualcomm.com
parent 0af2f6be

drivers/pci/of.c

+44 −0
Original line number Diff line number Diff line
@@ -966,3 +966,47 @@ 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 @presets structure.

 * Else, assign a default value of PCI_EQ_RESV.

 *

 * Return: 0 if the property is not available or successfully parsed else

 * 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 - 1; 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);

drivers/pci/pci.h

+31 −1
Original line number Diff line number Diff line
@@ -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 */
@@ -876,6 +878,21 @@ 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_8GTS,

	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 - 1][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);
@@ -890,7 +907,9 @@ 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)
@@ -935,6 +954,17 @@ 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)

{

	presets->eq_presets_8gts[0] = PCI_EQ_RESV;

	for (int i = 0; i < EQ_PRESET_TYPE_MAX - 1; i++)

		presets->eq_presets_Ngts[i][0] = PCI_EQ_RESV;



	return 0;

}

#endif /* CONFIG_OF */



struct of_changeset;