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[PATCH 2/4] PCI: of: Add API to retrieve equalization presets from device tree

Krishna chaitanya chundru posted 4 patches 1 week, 2 days ago
[PATCH 2/4] PCI: of: Add API to retrieve equalization presets from device tree
Posted by Krishna chaitanya chundru 1 week, 2 days ago 
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;

-- 
2.34.1
Re: [PATCH 2/4] PCI: of: Add API to retrieve equalization presets from device tree
Posted by Konrad Dybcio 1 week, 2 days ago 
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

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