On 25.01.2025 1:47 PM, Konrad Dybcio wrote:
> 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;
Also please #define 0xff as a reserved value
Konrad
>> + 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
