public-mirrors/linux
1
0
Fork 0
mirror of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2025-09-18 22:14:16 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions

PCI: of: Add of_pci_get_equalization_presets() API

Browse source 
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: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://patch.msgid.link/20250328-preset_v6-v9-2-22cfa0490518@oss.qualcomm.com
This commit is contained in:
Krishna Chaitanya Chundru 2025-03-28 15:58:30 +05:30 • committed by Manivannan Sadhasivam
parent 0af2f6be1b
commit 57a4591df7
2 changed files with 75 additions and 1 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

44
drivers/pci/of.c
View file

@ -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);

32
drivers/pci/pci.h
View file

@ -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;