On Thursday 24 February 2022 14:47:15 Bjorn Helgaas wrote: > On Tue, Feb 22, 2022 at 05:31:56PM +0100, Pali Rohár wrote: > > 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@xxxxxxxxxx> > > Signed-off-by: Marek Behún <kabel@xxxxxxxxxx> > > Reviewed-by: Rob Herring <robh@xxxxxxxxxx> > > Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> > > --- > > 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 cb2e8351c2cc..2b0c0a3641a8 100644 > > --- a/drivers/pci/of.c > > +++ b/drivers/pci/of.c > > @@ -633,3 +633,67 @@ 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; > > Including "mw" or similar reference to the units would give a hint of > how to relate the code to the spec. > > > + 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 */ > > Add a spec reference to PCIe r6.0, sec 7.5.3.9. IIUC, this supports > up to 300W, which was what r5.0 defined, but r6.0 added values up to > 0xfe (600W). I did not know about it and I have not seen/read r6.0. It would be nice if somebody with access to r6.0 send a patch to lspci utility, so we could write support for 600W based on lspci parser. > > + 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; > > If "slot-power-limit-milliwatt" contains a value larger than can be > represented in "value" and "scale", the return value will not agree > with value/scale, will it? In previous version 0xF2 was reserved for values above 275 W. So for me it looked like a correct solution. > Currently you only use the return value for a log message, so no real > harm yet, other than the fact that we might print "Slot power limit > 1000.0W" when the hardware will only advertise 600W available. > > Also, if "slot-power-limit-milliwatt" contains something like > 260000 mW (260 W), we'll return 0xF1/0, so the hardware will > advertise 275 W available. There is no way how to encode 260 W. It is possible only 250 W or 275 W, and nothing between. I chose to round value to upper limit. What do you prefer in these cases? Upper or lower limit? > > +} > > +EXPORT_SYMBOL_GPL(of_pci_get_slot_power_limit); > > diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h > > index 3d60cabde1a1..e10cdec6c56e 100644 > > --- a/drivers/pci/pci.h > > +++ b/drivers/pci/pci.h > > @@ -627,6 +627,9 @@ 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); > > @@ -653,6 +656,18 @@ 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) { } > > -- > > 2.20.1 > >