On Monday 11 April 2022 13:14:07 Pali Rohár wrote: > On Friday 08 April 2022 10:27:50 Bjorn Helgaas wrote: > > On Fri, Mar 25, 2022 at 10:38:26AM +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> > > > --- > > > Changes in v3: > > > * Set 600 W when DT slot-power-limit-milliwatt > 600 W > > > Changes in v2: > > > * Added support for PCIe 6.0 slot power limit encodings > > > * Round down slot power limit value > > > --- > > > 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..5ebff26edd41 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_mw; > > > + u8 value, scale; > > > + > > > + if (of_property_read_u32(node, "slot-power-limit-milliwatt", > > > + &slot_power_limit_mw)) > > > + slot_power_limit_mw = 0; > > > + > > > + /* Calculate Slot Power Limit Value and Slot Power Limit Scale */ > > > + if (slot_power_limit_mw == 0) { > > > + value = 0x00; > > > + scale = 0; > > > + } else if (slot_power_limit_mw <= 255) { > > > + value = slot_power_limit_mw; > > > + scale = 3; > > > + } else if (slot_power_limit_mw <= 255*10) { > > > + value = slot_power_limit_mw / 10; > > > + scale = 2; > > > + } else if (slot_power_limit_mw <= 255*100) { > > > + value = slot_power_limit_mw / 100; > > > + scale = 1; > > > + } else if (slot_power_limit_mw <= 239*1000) { > > > + value = slot_power_limit_mw / 1000; > > > + scale = 0; > > > + } else if (slot_power_limit_mw <= 250*1000) { > > > + value = 0xF0; > > > + scale = 0; > > > > I think the spec is poorly worded here. PCIe r6.0, sec 7.5.3.9, says: > > > > F0h > 239 W and <= 250 W Slot Power Limit > > > > I don't think it's meaningful for the spec to include a range here. > > The amount of power the slot can supply has a single maximum. I > > suspect the *intent* of F0h/00b is that a device in the slot may > > consume up to 250W. > > > > Your code above would mean that slot_power_limit_mw == 245,000 would > > cause the slot to advertise F0h/00b (250W), which seems wrong. > > So for slot_power_limit_mw == 245 W we should set following values? > > slot_power_limit_mw = 239 W > value = 0xF0 > scale = 0 I changed it in v4 > > I think we should do something like this instead: > > > > scale = 0; > > if (slot_power_limit_mw >= 600*1000) { > > value = 0xFE; > > slot_power_limit_mw = 600*1000; > > } else if (slot_power_limit_mw >= 575*1000) { > > value = 0xFD; > > slot_power_limit_mw = 575*1000; > > } ... > > This is already implemented in branch: > > } else if (slot_power_limit_mw <= 600*1000) { > value = 0xF0 + (slot_power_limit_mw / 1000 - 250) / 25; > scale = 0; > > I will just add reducing of final slot_power_limit_mw value. > > > I raised an issue with the PCI SIG about this. > > > > > + } else if (slot_power_limit_mw <= 600*1000) { > > > + value = 0xF0 + (slot_power_limit_mw / 1000 - 250) / 25; > > > + scale = 0; > > > + } else { > > > + value = 0xFE; > > > + 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_mw; > > > > If the DT tells us 800W is available, we'll store (FEh/00b), which > > means the slot can advertise to a downstream device that 600W is > > available. I think that's correct, since the current spec doesn't > > provide a way to encode any value larger than 600W. > > > > But the function still returns 800,000 mW, which means the next patch will > > print: > > > > %s: Slot power limit 800.0W > > > > even though it programs Slot Capabilities to advertise 600W. > > That's why I suggested setting slot_power_limit_mw = 600*1000 above. > > Ok, I will update slot_power_limit_mw value in next patch version. And also fixed this in v4. Please review v4 if is is OK now. > > > +} > > > +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 > > > > > > > > > _______________________________________________ > > > linux-arm-kernel mailing list > > > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > > > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel