On 24.01.2025 12:22 PM, 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@xxxxxxxxxxxxxxxx>
> ---
> drivers/pci/of.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
> drivers/pci/pci.h | 24 +++++++++++++++++++++++-
> 2 files changed, 70 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> index dacea3fc5128..7aa17c0042c5 100644
> --- a/drivers/pci/of.c
> +++ b/drivers/pci/of.c
> @@ -826,3 +826,50 @@ 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
> + * assign default value 0xff to indicate property is not present.
> + *
> + * If the property is not found or is invalid, returns 0.
> + */
> +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] = 0xff;
> + if (of_property_present(dev->of_node, "eq-presets-8gts")) {
> + ret = of_property_read_u16_array(dev->of_node, "eq-presets-8gts",
> + presets->eq_presets_8gts, num_lanes);
> + if (ret) {
> + 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] = 0xff;
> + snprintf(name, sizeof(name), "eq-presets-%dgts", 8 << (i + 1));
> + if (of_property_present(dev->of_node, name)) {
of_property_count_u8_elems returns -EINVAL if the property does not exist
you can then drop a level of indentation:
ret = of_property_read_u8_array...;
if (ret == -EINVAL) {
continue;
} else {
...
}
similarly above for 8gts
Konrad
