On Mon, Dec 23, 2024 at 12:21:15PM +0530, 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 | 45 +++++++++++++++++++++++++++++++++++++++++++++
> drivers/pci/pci.h | 17 +++++++++++++++--
> 2 files changed, 60 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> index dacea3fc5128..99e0e7ae12e9 100644
> --- a/drivers/pci/of.c
> +++ b/drivers/pci/of.c
> @@ -826,3 +826,48 @@ 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);
> +
kerneldoc? Define who should free the memory and how.
> +int of_pci_get_equalization_presets(struct device *dev,
> + struct pci_eq_presets *presets,
> + int num_lanes)
> +{
> + char name[20];
> + void **preset;
> + void *temp;
> + 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;
> + }
> + }
> +
> + for (int i = 1; i < sizeof(struct pci_eq_presets) / sizeof(void *); i++) {
> + snprintf(name, sizeof(name), "eq-presets-%dgts", 8 << i);
> + if (of_property_present(dev->of_node, name)) {
> + temp = devm_kzalloc(dev, sizeof(u8) * num_lanes, GFP_KERNEL);
> + if (!temp)
> + return -ENOMEM;
> +
> + ret = of_property_read_u8_array(dev->of_node, name,
> + temp, num_lanes);
> + if (ret) {
> + dev_err(dev, "Error %s %d\n", name, ret);
> + return ret;
> + }
> +
> + preset = (void **)((u8 *)presets + i * sizeof(void *));
Ugh.
> + *preset = temp;
> + }
> + }
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(of_pci_get_equalization_presets);
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 14d00ce45bfa..82362d58bedc 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 {
> + void *eq_presets_8gts;
> + void *eq_presets_16gts;
> + void *eq_presets_32gts;
> + void *eq_presets_64gts;
Why are all of those void*? 8gts is u16*, all other are u8*.
> +};
Empty lines before and after the struct definition.
> #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);
Keep the empty line.
> #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 inline 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
>
--
With best wishes
Dmitry
