Re: [PATCH dt + pci 2/2] PCI: Add function for parsing `slot-power-limit-milliwatt` DT property

[Bjorn Helgaas <helgaas@kernel.org>]

On Sun, Oct 31, 2021 at 04:07:06PM +0100, Marek Behún wrote:
> From: Pali Rohár <pali@kernel.org>
> 
> Add function of_pci_get_slot_power_limit(), which parses the
> `slot-power-limit-milliwatt` DT property, returning the value in
> milliwatts and in format ready for the PCIe Slot Capabilities Register.
> 
> Signed-off-by: Pali Rohár <pali@kernel.org>
> Signed-off-by: Marek Behún <kabel@kernel.org>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

Do we have a caller of of_pci_get_slot_power_limit() yet?  I didn't
see one from a quick look
(https://lore.kernel.org/linux-pci/?q=b%3Aof_pci_get_slot_power_limit).

Let's merge this when we have a user for it.

> ---
>  drivers/pci/of.c  | 64 +++++++++++++++++++++++++++++++++++++++++++++++
>  drivers/pci/pci.h | 15 +++++++++++
>  2 files changed, 79 insertions(+)
> 
> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> index d84381ce82b5..9c1a38d5dd99 100644
> --- a/drivers/pci/of.c
> +++ b/drivers/pci/of.c
> @@ -627,3 +627,67 @@ int of_pci_get_max_link_speed(struct device_node *node)
>  	return max_link_speed;
>  }
>  EXPORT_SYMBOL_GPL(of_pci_get_max_link_speed);
> +
> +/**
> + * of_pci_get_slot_power_limit - Parses the "slot-power-limit-milliwatt"
> + *				 property.
> + *
> + * @node: device tree node with the slot power limit information
> + * @slot_power_limit_value: pointer where the value should be stored in PCIe
> + *			    Slot Capabilities Register format
> + * @slot_power_limit_scale: pointer where the scale should be stored in PCIe
> + *			    Slot Capabilities Register format
> + *
> + * Returns the slot power limit in milliwatts and if @slot_power_limit_value
> + * and @slot_power_limit_scale pointers are non-NULL, fills in the value and
> + * scale in format used by PCIe Slot Capabilities Register.
> + *
> + * If the property is not found or is invalid, returns 0.
> + */
> +u32 of_pci_get_slot_power_limit(struct device_node *node,
> +				u8 *slot_power_limit_value,
> +				u8 *slot_power_limit_scale)
> +{
> +	u32 slot_power_limit;
> +	u8 value, scale;
> +
> +	if (of_property_read_u32(node, "slot-power-limit-milliwatt",
> +				 &slot_power_limit))
> +		slot_power_limit = 0;
> +
> +	/* Calculate Slot Power Limit Value and Slot Power Limit Scale */
> +	if (slot_power_limit == 0) {
> +		value = 0x00;
> +		scale = 0;
> +	} else if (slot_power_limit <= 255) {
> +		value = slot_power_limit;
> +		scale = 3;
> +	} else if (slot_power_limit <= 255*10) {
> +		value = slot_power_limit / 10;
> +		scale = 2;
> +	} else if (slot_power_limit <= 255*100) {
> +		value = slot_power_limit / 100;
> +		scale = 1;
> +	} else if (slot_power_limit <= 239*1000) {
> +		value = slot_power_limit / 1000;
> +		scale = 0;
> +	} else if (slot_power_limit <= 250*1000) {
> +		value = 0xF0;
> +		scale = 0;
> +	} else if (slot_power_limit <= 275*1000) {
> +		value = 0xF1;
> +		scale = 0;
> +	} else {
> +		value = 0xF2;
> +		scale = 0;
> +	}
> +
> +	if (slot_power_limit_value)
> +		*slot_power_limit_value = value;
> +
> +	if (slot_power_limit_scale)
> +		*slot_power_limit_scale = scale;
> +
> +	return slot_power_limit;
> +}
> +EXPORT_SYMBOL_GPL(of_pci_get_slot_power_limit);
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 1cce56c2aea0..9352278141be 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -665,6 +665,9 @@ struct device_node;
>  int of_pci_parse_bus_range(struct device_node *node, struct resource *res);
>  int of_get_pci_domain_nr(struct device_node *node);
>  int of_pci_get_max_link_speed(struct device_node *node);
> +u32 of_pci_get_slot_power_limit(struct device_node *node,
> +				u8 *slot_power_limit_value,
> +				u8 *slot_power_limit_scale);
>  void pci_set_of_node(struct pci_dev *dev);
>  void pci_release_of_node(struct pci_dev *dev);
>  void pci_set_bus_of_node(struct pci_bus *bus);
> @@ -691,6 +694,18 @@ of_pci_get_max_link_speed(struct device_node *node)
>  	return -EINVAL;
>  }
>  
> +static inline u32
> +of_pci_get_slot_power_limit(struct device_node *node,
> +			    u8 *slot_power_limit_value,
> +			    u8 *slot_power_limit_scale)
> +{
> +	if (slot_power_limit_value)
> +		*slot_power_limit_value = 0;
> +	if (slot_power_limit_scale)
> +		*slot_power_limit_scale = 0;
> +	return 0;
> +}
> +
>  static inline void pci_set_of_node(struct pci_dev *dev) { }
>  static inline void pci_release_of_node(struct pci_dev *dev) { }
>  static inline void pci_set_bus_of_node(struct pci_bus *bus) { }
> -- 
> 2.32.0
>