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 <quic_krichai@quicinc.com>
---
drivers/pci/of.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
drivers/pci/pci.h | 17 +++++++++++++--
2 files changed, 77 insertions(+), 2 deletions(-)
diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index dacea3fc5128..0d37bc231956 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -826,3 +826,65 @@ 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);
+
+int of_pci_get_equalization_presets(struct device *dev,
+ struct pci_eq_presets *presets,
+ int num_lanes)
+{
+ int ret;
+
+ if (of_property_present(dev->of_node, "eq-presets-8gts")) {
+ presets->eq_presets_8gts = devm_kzalloc(dev, sizeof(u16) * num_lanes, GFP_KERNEL);
+ if (!presets->eq_presets_8gts)
+ return -ENOMEM;
+
+ 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;
+ }
+ }
+
+ if (of_property_present(dev->of_node, "eq-presets-16gts")) {
+ presets->eq_presets_16gts = devm_kzalloc(dev, sizeof(u8) * num_lanes, GFP_KERNEL);
+ if (!presets->eq_presets_16gts)
+ return -ENOMEM;
+
+ ret = of_property_read_u8_array(dev->of_node, "eq-presets-16gts",
+ presets->eq_presets_16gts, num_lanes);
+ if (ret) {
+ dev_err(dev, "Error reading eq-presets-16gts %d\n", ret);
+ return ret;
+ }
+ }
+
+ if (of_property_present(dev->of_node, "eq-presets-32gts")) {
+ presets->eq_presets_32gts = devm_kzalloc(dev, sizeof(u8) * num_lanes, GFP_KERNEL);
+ if (!presets->eq_presets_32gts)
+ return -ENOMEM;
+
+ ret = of_property_read_u8_array(dev->of_node, "eq-presets-32gts",
+ presets->eq_presets_32gts, num_lanes);
+ if (ret) {
+ dev_err(dev, "Error reading eq-presets-32gts %d\n", ret);
+ return ret;
+ }
+ }
+
+ if (of_property_present(dev->of_node, "eq-presets-64gts")) {
+ presets->eq_presets_64gts = devm_kzalloc(dev, sizeof(u8) * num_lanes, GFP_KERNEL);
+ if (!presets->eq_presets_64gts)
+ return -ENOMEM;
+
+ ret = of_property_read_u8_array(dev->of_node, "eq-presets-64gts",
+ presets->eq_presets_64gts, num_lanes);
+ if (ret) {
+ dev_err(dev, "Error reading eq-presets-64gts %d\n", 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 14d00ce45bfa..757872f0cc35 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -731,7 +731,12 @@ static inline u64 pci_rebar_size_to_bytes(int size)
}
struct device_node;
-
+struct pci_eq_presets {
+ u16 *eq_presets_8gts;
+ u8 *eq_presets_16gts;
+ u8 *eq_presets_32gts;
+ u8 *eq_presets_64gts;
+};
#ifdef CONFIG_OF
int of_pci_parse_bus_range(struct device_node *node, struct resource *res);
int of_get_pci_domain_nr(struct device_node *node);
@@ -746,7 +751,9 @@ void pci_set_bus_of_node(struct pci_bus *bus);
void pci_release_bus_of_node(struct pci_bus *bus);
int devm_of_pci_bridge_init(struct device *dev, struct pci_host_bridge *bridge);
-
+int of_pci_get_equalization_presets(struct device *dev,
+ struct pci_eq_presets *presets,
+ int num_lanes);
#else
static inline int
of_pci_parse_bus_range(struct device_node *node, struct resource *res)
@@ -793,6 +800,12 @@ static inline int devm_of_pci_bridge_init(struct device *dev, struct pci_host_br
return 0;
}
+static 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;
--
2.34.1On 16.11.2024 2:37 AM, 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 <quic_krichai@quicinc.com>
> ---
> drivers/pci/of.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> drivers/pci/pci.h | 17 +++++++++++++--
> 2 files changed, 77 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> index dacea3fc5128..0d37bc231956 100644
> --- a/drivers/pci/of.c
> +++ b/drivers/pci/of.c
> @@ -826,3 +826,65 @@ 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);
> +
> +int of_pci_get_equalization_presets(struct device *dev,
> + struct pci_eq_presets *presets,
> + int num_lanes)
> +{
> + int ret;
> +
> + if (of_property_present(dev->of_node, "eq-presets-8gts")) {
> + presets->eq_presets_8gts = devm_kzalloc(dev, sizeof(u16) * num_lanes, GFP_KERNEL);
> + if (!presets->eq_presets_8gts)
If you make this an array with enum indices, you can make a for loop and
read "eq-presets-%ugts", (8 << i)
Konrad
On 11/16/2024 4:29 PM, Konrad Dybcio wrote:
> On 16.11.2024 2:37 AM, 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 <quic_krichai@quicinc.com>
>> ---
>> drivers/pci/of.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>> drivers/pci/pci.h | 17 +++++++++++++--
>> 2 files changed, 77 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
>> index dacea3fc5128..0d37bc231956 100644
>> --- a/drivers/pci/of.c
>> +++ b/drivers/pci/of.c
>> @@ -826,3 +826,65 @@ 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);
>> +
>> +int of_pci_get_equalization_presets(struct device *dev,
>> + struct pci_eq_presets *presets,
>> + int num_lanes)
>> +{
>> + int ret;
>> +
>> + if (of_property_present(dev->of_node, "eq-presets-8gts")) {
>> + presets->eq_presets_8gts = devm_kzalloc(dev, sizeof(u16) * num_lanes, GFP_KERNEL);
>> + if (!presets->eq_presets_8gts)
>
> If you make this an array with enum indices, you can make a for loop and
> read "eq-presets-%ugts", (8 << i)
>
> Konrad
as "eq-presets-8gts" is u16 array and other properties are u8 array.
I will use as it is for "eq-presets-8gts", but for remaining properties
I will use for loop as suggested by you.
- Krishna Chaitanya.
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